SelectableNode directly derives from ObservedSelectable instead of wrapping every single method.
Move ObservedSelectable to separate header file.
BrushNodes directly derive from ObservedSelectable now.
PatchNodes directly derive from ObservedSelectable now
Refactor PatchControlInstance to derive from ObservedSelectable
Minor refactoring.
Like Entities, PatchNodes derive from SelectableNode now.
BrushNode derives from SelectableNode too.

Fix qualified method calls.
Remove old BrushInstanceVisitor class.
Move SelectableBool to BasicSelectable.h
Move ClosestTexturableFinder to separate file pair.
Move OccludeSelector to separate header.