I've put the master/slave protocol in place. Uncommenting the code in
initExtension and chrome.tabs.onUpdated will activate master/slave mode.
It simply prompts the user to state whether they are a master or slave
and only sends update messages for masters.

However, I've noticed a bug with the launchedTab code. It seems
occasionaly that a tab's ID will randomly change, causing the extension
to prevent all update messages. I'm currently researching the issue.