Fix inconsistent replayq behavior, by adding new menu entry to globally replay audio

This fixes an inconsistency in the autoplay behavior between Anki Desktop and AnkiDroid, where the question was automatically replayed when `replayq` was set. A "replay audio" entry is added to the menu in the reviewer using the code from @ospalh, which does respect this `replayq` setting, but for now we keep the new menu item hidden due to a bug where cascading audio like this fails. I've created a [new issue 2084](https://code.google.com/p/ankidroid/issues/detail?id=2084) for this cascading audio bug. 

@chajadan I think this is one of your areas of expertise; would you mind taking a look at issue 2084? Once 2084 is fixed, we can re-enable the replay audio menu entry, and maybe add some preferences to remove the embedded play buttons, and/or promote replay to the action bar.

see #284 for more details