Add option for setting an event as recurring

[Frewacom]

Some events happen regularly, e.g. lunch. To make this easier to manage, student nations should be able to mark an event as recurring.

[McFrappe]

A flag for the event model might fix this... unless some magic with the DateTime or similar.
Hm i wonder if it would be enough to do the following algorithm:

• everyday, at a specific time, check for the events that has already occured (from the day before)
• If they have occured, then remove them or display them as "occured" or similar.
• If an event has a flag that informs this check that it is a reacurring event, then it does not bother with it and continues along to check other events for their dates.

Anything else one might add to this?

[McFrappe]

Commit 0dd6e0e