Optimize getValue
Track the view being activated for activated event
Short circuit helper append event if NOP
Cache the layout view element

Conflicts:
	src/layout.js
Implement collection element caching
Only register helper append handler when needed
Optimize noop path for renderTemplate
Avoid intermediate previousHelpers object creation

Calling _.without on the _previousHelpers field created a fair amount of unnecessary GC pressure. Instead adding a flag to the view instance to mark those that were not used in the render process.
Conflicts:
	src/helper-view.js
	src/thorax.js
Further optimization of walkInheritTree
Fix previous view cleanup
Rename _expectTemp to _pendingAppend