Feature Request: Allow approval of events in calendar #38

This is a feature request to support approval for events in the calendar app. The first and main purpose would be to create a vacation approval system.

Employee could create the vacation event in a group holiday calendar for their team, and the approver(s) could approve it.

I sure with some thought other use cases could be found, e.g. it could work for approving the use of some resource for a period of time, like a piece of equipment or something like this.