Added new Action Messages for Confbridge and MixMonitor

    - Includes ConfbridgeMute, ConfbridgeUnmute, MixMonitor, and
    StopMixMonitor.
    - Also updates tests and README
Fixes typos in DocBlocks; tests StopMixMonitorAction::setMixMonitorId
Merge pull request #54 from mstyles/mstyles_mixmonitor_actions

Adds new Action Messages for Confbridge and MixMonitor (revised)