Add an API to intercept when the content is changed when the Transition property is set to null.

To reproduce this, use 2 or more instances of a view with RadBusyIndicator in its contents. Then switch the contents of the TransitionControl using the two instances. This brings a slight glitch in the animation. The start width of the animated element gets stretched which should not happen in most animations. 

To work this around, instead of using the RadBusyIndicator as the content of RadTransitionControl, you can wrap the TransitionControl in a BusyIndicator.

 

The transition control is nice, but because it is triggered strictly by content changes, it is limited to pretty specific scenarios.  I suspect the transition code could work in many more scenarios, it if just knew when to trigger.  So this is my proposal: add a BeginUpdate function that would freeze a copy of the content, and an EndUpdate function that would then transition from the frozen copy to the current content.  In between the BeginUpdate and EndUpdate, one could make as many changes as needed to the content, without having to actually replace the content.  

Available in LIB version 2015.3.1123, it will also be available in the 2016 Q1 release.