plugin text commands: refactoring, text now only contain main commands, and other plugin can add commands themselve: - registerTextCommands can be called by a plugin in its __init__ method, it looks for methods starting with "cmd_" and register them as new commands - addWhoIsCb: add a callback to /whois command, the callback can complete whois informations - plugins parrot, XEP-0045 and XEP-0092 now manage their own commands