Polish for VBCaptionController

Closes #22

- Modularizes caption controller methods
- Adds failsafe for mike failure
- Adds styling to textview for caption controller
- Scrolls to bottom of text view content on new content arrival
- Clears caption history on source change
- Implements auto scroll to bottom on new captions
- Imports camera changes to caption view from master
- Adds animation and springs for caption resizing
- Re-adds camera capture session + preview to caption controller
- Forces camera view to take up full screen
- Reimplements publish of user images, only when user is checked in
- Adds active camera view for switching between local and remote cameras
- Applies camera capture image to caption screen for subscribed sources