Adds new Action Messages for Confbridge and MixMonitor (revised)

Adds Action Messages for the following Asterisk AMI actions:
https://wiki.asterisk.org/wiki/display/AST/Asterisk+10+ManagerAction_ConfbridgeMute
https://wiki.asterisk.org/wiki/display/AST/Asterisk+10+ManagerAction_ConfbridgeUnmute
https://wiki.asterisk.org/wiki/display/AST/Asterisk+11+ManagerAction_MixMonitor
https://wiki.asterisk.org/wiki/display/AST/Asterisk+11+ManagerAction_StopMixMonitor