DON'T MERGE: Arjen timeline refactor

### Problem
Timeline is too complicated.

### Solution
Start fixing based on https://github.com/nens/lizard-nxt/issues/295

* [ ] Timeline is always visible
* [ ] Calculate global aggregation window
* [ ] Snap time start and end to logical dates based on current aggregation window
* [ ] Replace brush for static aggregation window
* [ ] Zoom buttons for time
* [ ] Adapt height of added events

**Bonus:**
* [ ] Refactor logic for event / rain intensity data to be consistent
* [ ] Design for data availability (get raster dates from raster-store / raster api)
* [ ] Check animation speed?