* Several changes related to button pressing on the Mycroft unit:
- Pressing the button when it isn't listening starts it listening
- Pressing the button when listening will stop the listen
- Added a mycroft.util.signal() mechanism for out-of-thread communication
- Pressing the button now creates an "buttonPress" signal from the Enclosure
- The viseme playback and aplay check for the 'buttonPress' signal to abort
- Removed "Sorry I didn't catch that", irritating during false activations

* Fixed spacing that pep8 yelled about