Add minor enhancements.

General design rules tab converted to nanoscale. A bit of refactorisation in via sizes. And build key is KICAD_NANOMETRE not KICAD_NANOMETRIC (as I stated in previous commit).

Added configuartion option KICAD_NANOMETRIC for this.
* With option set to false: *
- it should work and compile as usual
- some values are saved with decimal point (which should be backward/forward compatible as old versions should just drop fractional part)
* With option set to true: *
- lengths in Global Design Rules should be settable 1nm steps.
FROM/TO_LEGACY_LU(_DBL) macros introduced for easy interconnection between old and new units.

* Use version of DateAndTime that returns a wxString and delete the
  version that takes a char* as it is no longer required.
* Merge StrNumICmp() and StrLenNumICmp() into StrLenNumCmp() to create a
  single function for comparing strings with integers and remove a lot
  of duplicate code.
* Remove unused strupper from string.cpp.
* Use wxArrayString for sorting the EDA_LIST_DIALOG contents.

Pcbnew: Fix a membar issue: Layer setup incorrect location (seems due to an error when using copy/paste editor command)

* Modify algorithm to correctly calculate the virtual drawing size and
  offset required to place the drawing correctly under all conditions.
* Ignore default wxWidgets scroll keys on Windows in EDA_DRAW_PANEL key
  event handler.

Fix bug 887202.

Lee algorithm replaced by a Minimun Spanning Tree algo (using Prim's algorithm ).
Tested on a 5350 pads board, it is more than 100 times faster.
Also fix a crash when clicking on tool  "delete selected items" (main horizontal toolbar),
and remove this tool (currently, no code in Pcbnew for this tool)

Pcbnew: connect.cpp: enhanced ( faster and more powerful ) algorithm to calculate connections between pads.
Code cleaning.

More about code refactoring in connect.cpp: RecalculateAllTracksNetcode() is 50 times faster with a board using 27000 tracks
Use right icon in pcbnew for load board and new board.

More work about code refactoring in connect.cpp

This first draft should fix bug 851670 and is faster than existing alogorithm.

Pcbnew: fix minor issue: Footprint bounding box was too large for very small footprints (like SM0204) due to the minimal size value used in  calculations.

* Create command event handler for orienting schematic items and block.
* Remove redundant orient item and block command handler code and IDs.
* Remove redundant cancel current command event table entry.
* Remove unnecessary schematic bitmap object virtual functions.
* Set path when saving schematic sheet files to prevent assertion in
  updated path and file write permission test function.
* Restore directory and file name write permission test function to it's
  previous behavior to prevent unexpected save results.
* Add an assertion to verify the path is not empty to directory and file
  write permission test function.
* Improve documentation for path and file write permission test function.
* Fix Doxygen link warnings.

* Change edit pin per part flag to only have effect when editing
  component with multiple parts or alternate body styles.
* Move global edit pin pert part variable into library editor frame
  object.
* Note that this only fixes the bug when the component does not have
  multiple parts or alternate body styles.

Fix erroneous test for non writable folder, when trying to save a schematic file with no path in name.
(seems wxFileName.IsDirWritable() fails under Windows when the path is empty (does not use the CWD).)

* Create command event handler for draggining all schematic items.
* Remove redundant delete item command handler code.
* Remove unused close current tool command ID from process special
  functions event handler.

* Create command event handler for editing all schematic and child items.
* Remove unique edit schematic item command IDs.
* Unify find item, undo, and redo hot key commands.

Now it select module from selected side if present. Especially handy in contrast view.

* Add a rotate event handler to schematic frame object.
* Remove unique rotate item command IDs.
* Use process event instead of post event to eliminate the need to clean
  up the command event client object from the heap.
* Unify find next item and next DRC error hot key commands.
* Unify move and rotate hot keys commands.

BOOST POLYGON is always used in zone filling functions.
Kbool is still in use in other calculations.

* Fix bug in draw reference for multiunit component
* Code cleanup for drag item

* Schematic fields now use unified move code.
* Move the unified move code into file schedit.cpp
* Remove old schematic field move code.

* Remove external dependency for adding suffix to reference designator
  fields.
* Make schematic field get and set position methods transform coordinates
  relative to the parent component object that owns them.
* Make base text class get text method virtual so derived classes can
  change the base string according to their individual requirements.
* Fix a problem with default place schematic item add in last commit.

* Tweak move item to support moving schematic sheet pin objects.
* Change schematic sheet pin set position to constrain position within
  the parent sheet.
* Schematic sheet pin moving now handled by unified move code.
* Remove old schematic sheet pin move code.
* Add custom client data object for passing hot key information to
  command event handlers.
* Fix a bug that prevented changes to schematic sheet pin objects from
  being undone.