BaseView invalidate() - use bit flags instead of booleans

[Swiley]

@benjaminbojko's idea In reference to BaseView's :
inline void invalidate(const bool transforms, const bool content);

"One idea I had just to keep for the future potentially was to use bit flags instead of booleans. That way we could add up to 32 options to invalidate and sub-classes could add their own. E.g. the FboView and TextView could use the same method."