Summary:
the bespoke parser was a horrendous drain on the build time of
plasma-desktop due to recursive templates.
it's been replaced with a new standalone binary that previews any
model/layout/variant/options combination as requested and a qtquick UI
which simplifies the actual rendering substantially.

the new code is better in that it:
- builds in a fraction of the time with a fraction of the power use
- renders complex models (such as the tm2020 or the kinesis) correctly
- because it entirely relies on xkb to figure out keysyms belonging to
  a given key, it's layout representation is not only substantially more
  complete it also correctly obeys options like eurosign:2
- renders numlock and the like (not that this is in fact very useful ^^)
- is following the system palette for coloring
- the paint code should be easier to graps and more robust because xkb
  provides completely consistent geometry and layout data meaning we can
  model this verbatim in qtq...