Fixes a bug in which registered 'rendered' callbacks are ignored and lost

Fixes bug in which 'rendered' callbacks registered on templates rendered through iron-router were overridden and lost when angular compile/digest cycle was incorporated.

This fix is implemented by caching any registered 'rendered' callback and then applying that callback after the angular compile/digest cycle is completed. After that, it then re-registers that cached function as the 'rendered' callback on the template.