Bug 1023663 - [User story] Calendar day view should start at 8 AM r=millermedeiros

Currently, the patch is for ui review. It is not ready for code review.
Actually, I prefer `ease` more than `linear`, and I will confirm this with Harly tomorrow. Using `linear` here is for comparing the performance with the JS implementation[1]. I think we could use `ease` here.

[1] https://github.com/evanxd/gaia/blob/bug-1023663-js-scrolling/apps/calendar/js/views/day_based.js#L654-L687