Merge branch '686-crash-when-transitioning-out-of-reblogactivity' into 'master'

Limit scene transition animations to API 23 and above

to work-around [android bug #224270](https://code.google.com/p/android/issues/detail?id=224270).
This is only necessary if the transitioning view might not be available anymore when the exit transition is made.

Closes #686

See merge request !361