Add support for registering for internal events like competitions.

[arungeorgesaji]

"Mods should be able to create events with the bot. Could we have a command like !createevent, where details such as the name, description, ID, etc., can be passed in? Then, users should be able to find events with a command like !findevents and register using !registerevent with the event ID. This can help streamline the process of hosting events."(maybe we could have smth like !myevents also to see what all events a user has registered for)