Add more new features and improve some existing ones.

* Add lightning effect event
* Extend the timer event to support repeating timers of fixed or random interval. Also made the minutes/seconds selected a bit more intuitive ;).
*Add arena join signs ([ems], arena name, [join]) which will make players join the arena when they click on it.
* Only allow join signs to be created when you have the arena which it if for open for edit
* Fix join signs so they also work with wall signs
* Add custom arena welcome and leave messages
* Remove debug in teamplayer count
* Fix your/you're typos