Dirk fix minor github issues

Minor fixes
--------------

- [x] remove no longer needed $watch for 'tools.active'
- [x] changed value suffix from "m" to "m NAP" used for overstort(ing)en : see https://github.com/nens/lizard-nxt/issues/293
- [x] repair CSV download for rain: see https://github.com/nens/lizard-nxt/issues/256
- [x] redraw rain graph bars when toggling timeline back on again: see https://github.com/nens/lizard-nxt/issues/282
- [x] Don't "cut off" x-axis labels for xy graphs (e.g: in the rain card)