Refactored stale callbacks cleaning logic in Future to support convenient zone.js patching.
Also fixed little bug with cleaning on `finally` call
optimized struct-template loading for the widget class with many instances
Profiler improvements:
* added basic version own async execution time metric (still need to be improved)
* added smart toJSON implementation to ProfilerTimer class
* fixed bug in onError callback
Profiler setup improvements:
* Implemented basic version zone.js support in Future (need to be refactored)
* Added couple of timers to core framework methods