vidforward: provide methods to save broadcastManager state to file

[Saxon Milton]

This will be important if there’s a crash and/or the virtual machine gets shut down for maintenance reasons on GCE’s side of things. We can invoke this whenever there’s a change in state and also on GCE shutdowns if we can work out how to respond to shutdown signals.

Vidforward Design Doc

[Saxon Milton]

Merged in state-save (pull request #493)

Resolves issue #386.

Add functionality for broadcastManager state save

→ <<cset 2da3d399d2a2>>