Kicad manager: code cleaning. Dead code removed and minor fixes. support of new .kicad_brd extension.

* Move EDA_TEXT object into separate header and source file.
* Compile EDA_TEXT class separately for BOARD_ITEM and SCH_ITEM units.
* Compile PAGE_INFO  class separately for BOARD_ITEM and SCH_ITEM units.
* Minor formatting tweaks to Pcbnew s-expression file.
* Move internal unit formatting functions into BOARD_ITEM and SCH_ITEM.

Enhancements in AddMenuItem (that accepts now a menu type)
Partial use of the Edwin van den Oetelaar's patch (patch not fully working or correct)

* Add s-expression Format() function to all objects derived from
  BOARD_ITEM.
* Add s-expression Format() function to base objects as required.
* Add functions to convert coordinates from base internal units
  (nanometers) to millimeter string for writing to s-expression
  file.
* Add temporary dummy conversion functions to prevent link errors
  until schematic and board object and action code can be separated
  into DSO/DLL.
* Add CMake build option to build Pcbnew with nanometer internal
  units.

Code cleaning and other minor fixes.

* EDA_DRAW_FRAME completely encapsulated except for DrawFrame member.
* Moved members specific to Pcbnew from EDA_DRAW_FRAME to PCB_BASE_FRAME
  or PCB_EDIT_FRAME as appropriate.
* Replace EDA_TOOLBAR with wxAuiToolBar as EDA_TOOL bar provided no
  additional functionality and made code less readable.
* Remove EDA_TOOLBAR class definition from wxstruct.h and delete file
  wineda_toolbar.cpp.
* Rename tool bar members to something more descriptive since the
  horizontal and vertical references wont mean anything once the
  tool bars are movable.
* Lots of dead code removal.

* Fixed bug on Windows that prevented the menu short cuts from working
  properly.
* Fix duplicate menu short cut keys in KiCad, Pcbnew, and Eeschema.
* Add menu short cuts for all possible menu entries.

* Correct all user strings and comments for the correct capitalization of
  application names according to JP.  They are KiCad, Pcbnew, CvPcb,
  Eeschema, and GerbView.
* Add a note the the user interface policy about the correct capitalization.

Fix compatibility issues with old xpm icons.
Add or update .xpm and .ico files for shortcuts and taskbars
Remove artwork folder.

Fix minor other issues.
Remove unused files.

* Added checks for Inkscape and pngcrush when MAINTAIN_PNG mode is enabled.
* Rebuild PNGs with transparent background.

Remove minizip from kicad sources. Useless because now (and since a long time) wxWidgets supports full zip file read/write, and minizip build creates problems under Windows, due to zlib not always installed.

* Rename all ADD_MENUITEM_* functions to AddMenuItem and move them to
  wxstruct.h since they are used by the Kicad main frame classes.
* Move SET_BITMAP and SETBITMAPS definitions to wxstruct.h.
* Fix a bug in SET_BITMAPS that prevented enabling menu item images on
  OSX.
* Rename MsgItem to EDA_MSG_ITEM.
* Remove redundant includes from modified files.
* Doxygen and coding style policy fixes.

* Check user write permissions before saving project file.
* Append read only to file name and path in title bar when the user
  does not have write privileges.
* Remove displaying file dialog every time the project file is saved.
* Doxygen comment and coding style policy fixes.

Minor fixes and enhancements.

Eeschema: optimize import of footprints names ( .stf files) that was time consumming with large designs.

* Remove most (not all) variables that were initialized but never used that
  cause GCC 4.6 to generate a warning.
* Fix bug in schematic library editor best zoom calculation.

fix an issue created by commit 2954. Gerbview: display now an indicator of layers in use. minor code cleanup.