Delete Message API, Live Event Log, Improvements & Bug Fixes

Added: Delete Message API - Allows the removal of a message via the API. (Read Delete Message documentation)  

Added: Live Event Log - Get a clear view of what's going on inside TalkJS in realtime. Did my REST call not arrive at all, or am I looking at the wrong user's Inbox? 

Added: Saving indicator whilst editing themes.

Improved: Dashboard navigation redesign which includes a clearer way to see if you're on Test or Live mode.

Several bug fixes.