Enable TTS_KEY_Q == TTS_KEY_A

Alters the newKeyHandler function to run either the front or back side
of a card using a single shortcut key.

This is handy when you have a set of cards where there is TTS on only
the front or back of each card, and you do not want to have to remember
which key to press to hear the playback again.

However, this feature does not work as expected if there is TTS on both
sides of cards. This is because there is currently no queue
implementation for playback (see issue imsys/AwesomeTTS#10 for more).