Zoom days in week, fix #65
Remarks:
- Should also be tested on slower devices. On my meizu pro 5(!) wild zooming has hiccups. While this does not happen on my laptop. I'm not sure how to improve this, but since it is thought to be used only occasionally and in an non-wild-manner, it's perhaps okay(?)
- zoom is not done around center - does someone mind that? :) Sure - it would be nicer if the zoom center would be respected...
- scrolling to next week does not work properly, if fully zoomed out (didn't get why yet), so the zoom out is restricted to 7 days minus epsilon