Arjen timeline refactor

### Problem
Timeline is too complicated.

### Solution
Start fixing based on https://github.com/nens/lizard-nxt/issues/295

* [x] Calculate seconds / pixel
* [x] Timeline is always visible
* [x] Calculate global aggregation window
* [x] Refactor  timeState
* [x] Replace brush for static aggregation window
* [x] Adapt height of added events
* [x] Move play button to Berto's place
* [x] Update, enter, exit for aggWindow drawing
* [x] Zoom buttons for time
* [x] Move zoomtonow button to nicer place
* [x] Fix 'today and future' indicator
* [x] Move timeState.at to nicer place
* [x] Display full start and end dates
* [ ] Translate start, now and end date in timeline to Dutch
* [x] Fix drawing events (vectors), remove circles, only do lines
* [x] Update docstrings & dev docs

**Bonus:**
* [ ] Update url
* [ ] Nicefy CSS / design / UX
* [x] Snap current aggregation window
* [ ] Fix offset in aggWindow and snapping