Eeschema, Libedit: Fix bug that can crashes Eeschema: In libedit 2 mandatory fields could be deleted. Fixed now.
Very minor other fixes.

* Derive the pcbnew copper zone and non-copper zone dialog windows from DIAG_SHIM,
  which injects some template code.
* Update UIpolicies.txt to talk about DIALOG_SHIM support.
* Add zone support to eagle_plugin.
* Organize ZONE_CONTAINER class declaration for future privacy and accessors.

 fix a compil warning.
CvPcb: fix regressions :
 Shows now a void field instead of the dummy footprint name $nonane (whenthere is  no footprint selected in netlist).
 The active footprint selection changes only if a new component is selected from the component file,
 and does not change just when the next component is automatically selected, after a footprint selection.
 Speed up delete association and auto associe.

Very minor code cleaning

Because this bug could create bad values in footprint libraries, this parameter is now checked
when reading a footprint description in legacy format

Pcbnew: fix Pcbnew name capitalization in messages.
About dialog: add a link to kicad-pcb.org

3D viewer: fix incorrect scaling factor when using nanometers.
Very minor other fixes

Fix some comments.  Enhance LEGACY_PLUGIN such that it can tolerate, then fix bad legacy footprint libraries containing duplicate footprint names.
This may have been an undocumented bug from more than a year ago, which manifested itself in *.mod files containing duplicate names.
LEGACY_PLUGIN loads those now quietly, but appends "_v2", "_v3", etc. to each succeeding duplicate sharing the same name.