Prevent multiple RenderAll calls on exit edit

This fix prevents ```renderAll()``` being called for each IText instance when ```exitingMode``` is exited.  Only one ```renderAll()``` is necessary
Prevent multiple RenderAll calls on exit edit

This commit modifies the ```mouseUp ```handler to fix ```enterEditing``` behaviour, while maintaining the ability to fire ```enterEditing()``` programmatically
Merge pull request #1110 from GordoRank/Fix-multiple-renderAll-when-exiting-editing-mode

Fix multiple renderAll when exiting editing mode