Moved View related routines & fields from PCB_{BASE,EDIT}_FRAME & BOARD to PCB_DRAW_PANEL_GAL.

Pcbnew: Rework on Gerber ouput: allows choice between format 4.5 and 4.6. Fix a minor issue in Gerber layers attributes.
fix print issue when printing each layer on a separate page.

Also a minor cosmetic enhancement in SVG export and plot dialogs.

The default layer stack between these 2 types was swaped in pad definition, and also in the dialog pad properties.
This double swap creates no bug, but creates bugs in the footprint wizards (SMD or CONN pads do not have the right layer stack)
FYI, the CONN pad type should be removed soon.

2) Change from legacy Cu stack to counting down from top=(F_Cu or 0).
   The old Cu stack required knowing the count of Cu layers to make
   sense of the layer number when converting to many exported file types.
   The new Cu stack is more commonly used, although ours still gives
   B_Cu a fixed number.
3) Introduce class LSET and enum LAYER_ID.
4) Change *.kicad_pcb file format version to 4 from 3.
5) Change fixed names Inner1_Cu-Inner14_Cu to In1_Cu-In30_Cu and their
   meanings are typically flipped.
6) Moved the #define LAYER_N_* stuff into legacy_plugin.cpp where they
   can die a quiet death, and switch to enum LAYER_ID symbols throughout.
7) Removed the LEGACY_PLUGIN::Save() and FootprintSave() functions.
   You will need to convert to the format immediately, *.kicad_pcb and
   *.kicad_mod (=pretty) since legacy format was never going to know
   about 32 Cu layers and additional technical layers and the reversed Cu
   stack.

Minor enhancements.

They are now member of EDA_DRAW_FRAME.
This change could fix Bug #1330781 (Background color change in Eeschema affects background color in Pcbnew)
Show page limits has meaning only for the schematic editor,  the board editor and the page layout editor.
Draw background color selection exists only in eeschema and  page layout editor.
In pcbnew, only a black background is allowed.
A side effect is now the user should set the background color in schematic editor, and the library editor (2 different options).
The default is still the white color.

Change class PROJECT to use a generalized wxString in place of the
RETAINED_PATH items, so that new session and project specific strings
of any purpose can be saved there, for the life of a session.

This workaround was already used (bzr 4301, in file plot_board_layers.cpp) also to avoid similar crashes (uses 18 segments instead of 16 to approximate a circle by segments).
Minor code cleanup in dialog_plot.

Fixes the bug that causes pcbnew crash, when there are multiple net classes and the plot dialog was opened.
Changed NETCLASS* to boost::shared_ptr<NETCLASS>.

Pcbnew: plot dialog: remove obscure and useless option about texts which are not value or reference.
cosmetic enhancement in dialog.
page layout: fix bug Bug #1320839 (canvas refresh countinously called when moving an item)

Most of the changes are just adding GetDesignSettings() before every occurence of m_NetClasses.
More complex changes:
class_netclass.cpp - NETCLASS does not store the pointer to the parent BOARD anymore. Added function SetParams( BOARD_DESIGN_SETTINGS& ).
class_netclass.h - Removed GetTrackMinWidth(), GetViaMinDiameter(), GetViaMinDrill(), GetuViaMinDiameter(), GetuViaMinDrill() as they were refering to BOARD_DESIGN_SETTINGS anyway (they are not net class specific).
kicad_plugin.cpp - filters out empty nets (that are anyway not saved) when storing net class information. Previously it was done in NETCLASS::Format() function.

In particular HitTest for zones *do not* select the nearest vertex/edge as a side effect

In particular HitTest for zones *do not* select the nearest vertex/edge as a side effect

- SEGVIA becomes VIA
- Drill size moved from TRACK to VIA
- Removed shape from TRACK, becomes ViaType in VIA
- GetTrace becomes GetTrack, for uniformity
- Some minor constification and typo fixes