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

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.

Changes introduced by the module editor are updated in GAL canvas.

DXF export: fix incorrect export of polygons having thick outline (like zones): Thick segments of outline were drawn like lines with no thickness.
Fix ( workaround only) crash (Windows only) when a quasi modal frame (like footprint viewer) was called from a dialog (like the component properties dialog in schematic editor).
Very minor other fixes.

Cursor position is saved as a field in order to avoid drifting of items while they are being dragged and rotated/flipped.

Resolved HOME hot key conflict between menu entry (Zoom Page) and event assigned to the hot key in the ACTION_MANAGER.
Conflicts:
	pcbnew/menubar_pcbframe.cpp

Added preference for selecting tracks/vias/graphics if there is a module present in the selection point.

- 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

Key events are handled by wxEVT_CHAR instead of wxEVT_KEY_[UP|DOWN]. Fixed issue of chars that require modifiers (e.g. ? is Shift+/ on US keyboard layout).

Hot keys specific to a tool have priority over global hot keys (TOOL_ACTION scope: AS_GLOBAL/AS_CONTEXT is finally handled properly).

Items that may be modified using EDIT_POINTs used to stay selected after pressing ESC (only EDIT_POINTs got away) - fixed.

Renamed [class_]drawpanel_gal.[cpp|h] to [class_]draw_panel_gal.[cpp|h] to follow current naming scheme.

Added possibility of switching tools by the right toolbar buttons, without deactivating the current tool first (previously tools did not switch if there was one active).