Fix GC finalizer issue

Fix GC finalizer issue

 - Finalizer was called in GC thread and it can't access EFL object
 - Remove all finalizer code that access EFL object
 - Hold the reference of EvasObject that was added on Window
 - Fix wrong IDispose implemention
   - When Dispose(false) native handle should be freed,
     but we didn't, it cause seg-fault, after released C# layer, native callback can invoked.
   - So, We release native handle when Dispose(false) was called.
   - but, it will cause some error message 'Maybe it has already been freed.'

Change-Id: Ic225799ac8cf9fd102a67d870043cb24bad55c7d