Introduce ModeProcessFlags, can be passed to ModeParser::Process() to indicate local only mode changes and mode merges

Change ProtocolInterface::SendMode() to take source and destination parameters, and call it from the mode parser whenever the mode change is global

This deprecates the ambiguous InspIRCd::SendMode() and InspIRCd::SendGlobalMode() interface (the latter sent mode changes originating from local users twice, etc.)
Replace void* dest and target_type parameters of OnMode with a User* and a Channel*