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.

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.

Show the "Description" field from fp-lib-table in pcbnew's module editor 'set current library' dialog.

Fix a very minor bug (2 duplicate lines when copying version informations to the clipboard)

columns.  DIALOG_SHIM would resize each separate usage to the same
size.  DIALOG_SHIM now supports and alternate m_hash_key in lieu
of the class name, optionally.