Implemented a nicer transition when the icons overflow

The overflowing icons are now represented as dots and
animate in and out nicer.
The shelf also animates much nicer from the regular statusbar
size if there are a lot of notifications.

Test: Add a lot of notifications, observe them nicely overflowing into dots
Bug: 32437839
Change-Id: I5906c076bbf5d48cbabdbacfd21234bed55c6caa