Create Events as entities to allow for multiple years

This (set of) module(s) comes closest to what I would need for a website administering conferences. That's - I must say - mostly due to the nice drag and drop scheduler functionality which is a particularly user-friendly way of rescheduling sessions/presentations.

However, I'm also looking for a solution that would allow me to manage multiple conferences organized by the same institution over a longer period of time. I'm looking forward to the development proposed in this issue as it would greatly enhance the functionality of this module.

The schedule tabs still aren't working as intended, but that could be worked on in a separate issue.

Personally I tend to think think this should be rolled into a new major version, because it will have no backwards compatibility with the current 1.x branches. Open to other perspectives, though.

Moving this to a new 2.0.x branch.

Merged in.