Previous visual changes in the library were quite limited with some
colors and some global properties. This commit changes all that and
provides way more control over every widgets visual appearance.
Changes include extended color selection, per widget properties and
the possibility to use skinning.
While the new API allows for a lot more control it is currently quite
low level and needs a lot more testing and probably another higher
level style API to make changes in code easier. I also had to remove
the style modification code inside the demo and will probably first
try to write another higher level API before adding it back in.
This commit also include some breaking changes to existing code like
the missing style stack API and some widget names changes due to
added granularity granted by the rewritten style.
fcba0e676b