Pcbnew: Fix incorrect behavior of undo/redo command (this issue happens only when a new track is created, and an old redundant track is deleted)
Minor code cleaning

  -wxSize         g_ModuleTextSize;      /* Default footprint texts size */
  -int            g_ModuleSegmentWidth;
  -int            g_ModuleTextWidth;

and add similarly named variables to BOARD_DESIGN_SETTINGS, which are 
in a BOARD.

Also commit updated icnos from Fabrizio.

support new zone field ZPriority in kicad_plugin.cpp, enhance TESTLINE() so it does not match substrings

Pcbnew: added a priority level for zones: a zone with a hight priority can be now inside an other low priority zone.
useful for complex zones.
fix in footprint copy.
minor enhancement in netlist/ Footprints Test.

Pcbnew: minor code change in netlist functions.

Pcbnew:  First draft to use a new netlist format ( containing the same info as the intermediate netlist, but using S expressions)
* Eeschema can generate this netlist format.
*   Pcbnew can use (automatic identification) the current format or the new format.
*   Cvpcb does not use yet the new format.

  * Enhance class PLUGIN's comments to improve their value as instructional.
  * Switch #includes from "file.h" to <file.h>, and fiddle with search paths
    by using include_directories(BEFORE ...)
  * dialog_page_settings did not have symmetrical space on its right border.
    And it now remembers it last position and size within a program session.
  * base_screen.cpp is now compiled twice, once for {pcbnew,cvpcb} and once
    for eeschema, in preparation for "compile time" support of internal units
    rather than "runtime" support.

compile base_screen.cpp separately for {pcbnew,cvpcb} and eeschema, so we can diverge internal units at compile time, not runtime

Pcbnew: 2 minor enhancements

Pcbnew: fix a serious bug: crashes when attempt to modify a zone that had lost its net (after eeschema changes for instance)

keep all the labelling tools together in the eeschema toolbar.

portrait setting was being overwritten in dialog_page_settings.cpp, add updatePortrait(), improve comments