In KIFACE_I::end_common save the 'common' configuration variables loaded in KIFACE_I::begin_common (the background color and the page border flag)

- Refactored the common part of cursor key movement and crosshair update
  in the various GeneralControl
- Add x10 movement with the keyboard (CTRL modifier)
- Avoid fixup of the cursor position by dummy mouse movements generated
  by cursor warping (original analysis and idea Chris Gibson)
- Do key handling in a way to permit sub-pixel cursor movement 

   to a new BOARD in the footprint editor.  This is PAGE_INFO::A4 and company.
   
*) Remove static storage of the BOARD in the module editor.

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.

remove global g_UserLibDirBuffer which was a project specific global, and no longer used with FP_LIB_TABLE support.

Pcbnew: fix a minor bug: in zones with no net, only the zone clerance was used to created clearence,  regardless the pad or footprint local clerance.
Very minor other fixes.

Minor refactoring of PAINTER & RENDER_SETTINGS classes.

A couple of trivial accessors made inline

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)

Pull unfilled polygon drawing thru the line clipper; GTK mess up even in this case and the sheet border lines glitch on the screen at high zoom otherwise in pcbnew.

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.

Moved background color settings from GAL to RENDER_SETTINGS. Added RENDER_SETTINGS::TranslateColor() to convert between EDA_COLOR_T and COLOR4D.

Moved menuCopy to CONTEXT_MENU copy constructor.

Added WX_UNIT_TEXT - wxWidget control for inputing sizes using different units (mm, inch, internal units).

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