Removes duplicated code and makes method easier to test

- Tests for TTS base class
- Test for TTS playback queue
- Test for TTS Factory create
- Tests for Mimic2 TTS
- Tests for Mimic TTS
- Tests for Google TTS

tts.py:
- remove unused import
-remove unused variable
- init TTS thread enclosure member
mimic2_tts.py: Fix docstrings
mimic_tts: Fix docstrings and remove unused variables and imports
google_tts: Improve docstrings

Add TTS tests

Disable failing spanish datetime test

This makes it possible for the installer skill to report errors during
install and remove of skills

Update msm to 0.8.5

This is more inline with the tests that are performed in the file.

This also adds a test for stop_speaking

This includes init, shutdown, play, stop, next, previous, pause,
seek_backward, seek_forward, queue lower_volume, restore_volume and resume.

Add tests for the audioservice interface

Add readthedocs docs for settings_change_callback

The message is sent when there are no more tracks in the queue and
playback has stopped.

Send mycroft.audio.queue_end