The default value for levelrequired is HALFOP_VALUE, meaning the ModeChannelVoice class is not required but it will be useful in case the default changes
- Type of the extension used to store data is a template parameter
- The extension is automatically unset when the mode is unset
- Handlers inheriting from ParamMode have to provide OnSet() and SerializeParam(); may optionally provide OnUnset()
- Transparently handle the case when OnSet() modifies the mode parameter
- Remove Channel::custom_mode_params map; ask the mode handlers to serialize their parameters instead
The function does not need to be virtual because the core can remove any user mode using the default logic
The optional modestack parameter was always NULL, so remove it
