Pcbnew:, libedit, Save lib as...: the new .pretty lib format is the default, instead of legacy .mod format. The legacy format is still selectable in the file selection dialog.

   To use multiple working threads.  This entailed adding KiCad typedefs:
*) Add typedefs for MUTEX and MUTLOCK which mask the actual choices for the project.
*) Add FOOTPRINT_LIST::DisplayErrors( wxWindow* ) which is a single strategy for
   showing aggregated load errors.  Although what's there is only scaffolding
   and needs a volunteer who knows HTML pretty well.
*) Ensure all callers of ReadFootprintFiles() use the new DisplayErrors() function.   
*) Push utf8.cpp and utf8.h into common library for open use.

* Make the tool bar dockable.
* Enable the overflow control in the tool bar in case the it does not fit in
  it's parent window.
* Fix some wxAuiPaneInfo usage issues.
* Remove unused wxAuiPaneInfo objects.
* Move perspective saving and loading into EDA_BASE_FRAME object in preparation
  for extending this to all frame windows.

Plot functions: some enhancements in mirror mode (Pcbnew specific): boards are mirrored horizontally, and the page layout is no more mirrored, and therefore is always readable.

Moved scaling of font glyphs to the moment when they are created (eliminated a few multiplications unnecessary variables).
Changed some magic numbers into constants.

Fixed SetCurrentContext() assert, that was firing on closure of pcbnew, when the OpenGL backend was active.

Pcbnew: fix issue in modedit, undo command: moved fields were not drawn afetr undo (due to incorrect flags state)
Fix incorrect initialization of lib names column in EDA_LIST_DIALOG. (Only the row 0 was initialized)

* Replace illegal file system characters when reading legacy libraries to
  prevent FPID parsing errors and allow saving to PRETTY file format.
* Create validator to filter illegal file system characters from footprint
  name text edit controls to prevent issues when saving to PRETTY file format.
* Add missing source file licenses and some minor coding policy fixes.

Now footprints, after loaded by reading a netlist are grouped by sheets by the footprints spread function, and the grouping is better.
Rename 2 files. Fix minor issues. Clean code

   comment for GITHUB_PLUGIN which should flow into Doxygen output.
*) Rewrote: 
        PCB_BASE_FRAME::Save_Module_In_Library(): now uses fp-lib-table and PROPERTIES.  
        PCB_EDIT_FRAME::ArchiveModulesOnBoard(): now can archive to any writable library type.
        PCB_BASE_FRAME::SelectLibrary(): is now generic for selecting a library, not just the active library.

Pcbnew: Code cleaning and bug fix in autoplace functions
Dialog exchange footprints has now a separate button to update the .cmp file, only on request.

FIX: unique renaming of eagle footprints by substituting illegal : and / with URL encoding technique.
ADD: window resize border to DisplayError() windows.

*) Save library nickname in APP so upon module editor re-entry last is re-used.
*) Fix bug editing fp-lib-table Description field.