Explicitly hide the soft keyboard on card flips. Quick fix for issue 2170.

I am still baffled why the addition of the navigation drawer should make the soft keyboard [*not* hide](https://code.google.com/p/ankidroid/issues/detail?id=2170).

Nonetheless, this is a quick fix that just hides the keyboard when we flip the card.

P.S.
This time i explicitly did not include the whitespace removal. That would clash with #405.