Modular-Kicad milestone B), minor portions:

*) KIWAY_PLAYER::IsModal() is now a retained state, controlled by SetModal()

*) Fully re-work the KIWAY_PLAYER::ShowModal() to use a nested event loop.

*) Add support to DIALOG_SHIM for a "quasi-modal" dialog presentation and mode.
   See top of dialog_shim.cpp about that for benefits and need.

*) You can now pick footprint from the schematic component field dialog, although
   if you do this before you open the BOARD, you will only get the global footprint
   libraries, not also the project specific ones.  Opening the BOARD first avoids this
   problem.

This is the first example of cross KIFACE invocation, it is also the first
instance of using a TOP_FRAME other than FRAME_PCB as the first thing. It works,
but it's missing support for opening the project specific table because
historically the FRAME_PCB did that. This is now starting to expose all the near
term needs for KIWAY_PLAYER <-> PROJECT interaction, independence and out of
sequence usage.

A fix for this will be coming in a few days.

However it mostly starts to show why the KIWAY is terribly useful and important.