Add Hold and Resume message sending from SPA to Conversation Window
Add a call state for hold, and handle the hold and resume messages, and muting of streams
Add notifications for a call being on hold; fix setting mute state
Fix lint failures
Handle correct hiding of the video and showing the text messages when a call is on hold.
Try Fix Travis failures in frontend chat tests.
Merge pull request #331 from Standard8/hold_resume_ui

Implement UI for when a call is placed on hold and resumed from an SPA