New event layout algorithm

[JonasWanke]

The current layout algorithm works and I like the behavior of overlapping events to save space, but there are few cases that aren't optimal. An example of that is #29 which is now fixed, but only with a suboptimal workaround.

I'd like to invest some time into designing a new algorithm that is a bit more flexible than grouping partially intersecting events and dividing them into columns. Some examples from another calendar with better layouts: