Bug 1072191, 1074613, 1072186 - Layout normalization follow-ups

- |LayoutLoader._normalizeLayout| is now delegated onto LayoutNormalizer
-- Alternativs chars normalization codes are moved to LayoutNormalizer
- LayoutNormalizer is no longer a singleton (better pattern since it's only used locally)
- textLayoutOverwrites is now normalized
- Layout keys are frozen after normalization (in normalizer) or creation (in LayoutManager)
Do we/should we/can we freeze the page objects as well, and all other objects inside the original layout?

(That probably depends which object we want to do deep copy and which object we want to continue use as prototype)