This is rather a handbook example how NOT to do things in SCons, ideally
it should be official SCons target so all the dependencies and source file
modification stops being our worry. Especially since for CMake we already
do have an app to do generate all the data.
I don't have time to clean this up now but this constant icons regeneration
just pisses me off atm.
this allows for updating icons without committing a new PNG each time
(which is inefficient with git). The data files are converted into a
PNG at builds time and used just as they were before.
