Factored out the next-pad-number function

Use environment KISYS3DMOD to know the default path for 3D shapes in footprint editors dialogs, and build short 3D file names.
This value is now shown in these dialogs.

If it is not defined by user, it is set to a legacy 3D files path.
The default value needs to be fixed on MACOSX.
This change could be better, but it is compatible with environment variables and the old way ( defined search paths) to find 3D shape files.
3D shapes files names can  also include an environment variable definition, like libraries names.
However using KYSYS3DMOD in these names is not required.
If the 3D filename is a legacy name, KYSYS3DMOD is automatically used as default path.

Add a workaround to fix a new bug in wxWidgets 3.0 ( Windows specific ) which shows icons only with a size = 16x16 in menus which have attribute wxITEM_CHECK

* Add Henner's patch (with minimal changes) to ensure CVpcb footprint view window is always brought into view, even after being hidden by another window

Fix some incorrect icons (which were using a not supported font for texts). Add ps_router icon from Konstantin Baranovskiy.