The brush server needed access to the KisResourceServerProvider singleton
in its constructor, while in the constructor of KisResourceServerProvider,
the loading of presets needed to have all the brushes loaded.

This commit moves libbrush to the krita/image and krita/ui level and
makes kritaui link to libbrush instead of the other way around. Now
we can load the brushes and then the presets.

This makes start a bit slower... But on the other hand, you cannot crash
Krita anymore by closing it while the presets are still being loaded.