remove IText _render()

The ```the _render()``` method for IText objects is no longer needed when since rendering cursor/selection is now handled elsewhere
Update renderCursor/renderSelection

Update renderCursor()/renderSelection() to draw to separate canvas
Update itext.class.js
update cache automatically in _set()
update cache in setElement()
revert
revert master
Optimize searchPossibleTargets
Move check into separate function
Iterate backwards
Merge pull request #1127 from GordoRank/Optimize-searchPossibleTargets-for-IText

Optimize searchPossibleTargets for I-text