fix issue #491 - opt-in/opt-out of scrollback per channel
Merge pull request #515 from Misdre/optin-optout-scrollback

fix issue #491 - opt-in/opt-out of scrollback per channel
Closes #290 - opt-out for extra alerts now working
Merge pull request #516 from Misdre/optout-extra-alerts

Closes #290 - opt-out for extra alerts now working