[Azoth MuC] Refactored common parts to PerformMucAction.
[Azoth MuC] Added /version, closes #1660.
[Azoth Xoox] Fixed entity time handling for MUC participants.
[Azoth] Added IHaveEntityTime::entityTimeUpdated() for #1657.
[Azoth MuC] Added /time command, closes #1657.