Pcbnew, dxf import: Add dialog to choose the board import layer, and the position of dxf coordinates origin

Fix issues created by this patch.
Note, this fix slightly changes the vertical position of these texts.
This is not really a  problem in eeschema, but in pcbnew this is perhaps  more annoying, if the verical multiline text is critical.
Fix a very minor issue  for vertical justification of single line texts in dxf import.

Pcbnew: First work to add a DXF file import to create board outlines. The DXF import is based on DXF lib import/export  from LibreCad.

more DIALOG_FP_PLUGIN_OPTIONS work, make PROPERTIES a map instead of a hashtable for alphabetical iteration.

*) Use it on 3 grids total in DIALOG_FP_PLUGIN_OPTIONS and DIALOG_FP_LIB_TABLE.
*) Fix bug when pasting "(fp_lib_table" text into FP_LIB_TABLE.

Page layout editor: Add bitmap items to the page layout existing items.
Now a bitmap image can be added to a page layout description. Currently the bitmap is expected having a 300 ppi definition.
Note: not all plotters can plot a bitmap, and in this case the bounding box is plotted instead of the bitmap

* Create a generic yes/no/cancel dialog from DIALOG_EXIT.
* Make DIALOG_EXIT return wxID_YES instead of wxID_OK so it is consistent
  with the standard message dialogs.
* Add missing license to confirm.h and confirm.cpp.
* Change Eeschema message dialog when loading a schematic if the current
  schematic is modified to be more consistent with the exit dialog.
* Change Pcbnew message dialog when loading a board if the current board
  is modified to be more consistent with the exit dialog.
* Remove some Eeschema block debug logging code left over from my last
  commit.

Add support for building *.deb file using CPack, install ~/fp-lib-table either from kicad-install.sh or from make install_user_configuration_files

* Merge HandleBlockEnd() and HandleBlockEndByPopUp() into as single block
  end function HandleBlockEnd().
* Replace all instances of HandleBlockEndByPopUp() with HandleBlockEnd().
* Change block hot keys to send command events instead of directly calling
  end block handler.

Temporarily disable Boost.Context library build as it breaks MinGW builds by bringing in a dependency on MASM (The Microsoft Assembler)

Planning for PCB_BASE_FRAME::Save_Module_In_Library and PCB_EDIT_FRAME::ArchiveModulesOnBoard rewrites

Pcbnew: Fix issue when displaying net names and/or pad numbers including the "<" char in drc dialog, because drc dialog uses an wxHtmlWindow to display drc messages, and the "<" char has a special meaning and is not allowed in texts (now replaced by the" &lt;" sequence in messages displayed in html)
Eeschema: replace "<" and ">" by "(" and ")" in autogenerated net names, to avoid other issues in html messages.
Very minor other fixes.

*) Set environment variable KISYSMOD before loading FP_LIB_TABLE so that
   FP_LIB_TABLE::ROW::SetFullURI() can do substitution up front.
*) De-emphasize the lib path in some of the footprint frames but keep it
   so the footprint editor can export a current library to another.
   You can even export a GITHUB library to a pretty library for local 
   installation.
*) Start the PLUGIN options editor.
*) Enhance cursor positioning in DIALOG_FP_LIB_TABLE.

specctra_export.cpp: fix a bug in my export function to 3D viewer which generates bad shapes for holes generated by outlines
inside the main board outlines.
specctra_export.cpp: always approximate arcs in outlines by 36 segm for 360 degrees,
even for arc angle which differs from 90 degrees.
90 degrees is the default when creating an arc, but the arc value can be edited and have any value between 0 and 360 degrees.
Previously, 9 segments were used regardless the arc angle.

* Add save table and set project path environment variable code to
  FP_LIB_TABLE object.
* Add code to Pcbnew and CvPcb to set project path environment variable.
* Create empty footprint table in Pcbnew when new board created.
* Save current project specific footprint library table to path on file save
  as or empty project path.
* Fix a bug in Pcbnew in file save function that would silently overwrite
  an existing board file.
* Disable selecting the current library in the module editor when there are
  no libraries defined.
* Catch exceptions and report errors when writing footprint library tables.
* Fix Boost build CMakeFile to fix bug when bootstrapping a Boost build in
  MSys.