Fix seeking behavior

A recent fix to seeking behavior injected a couple of issues that need
to be addressed:
- the start time should be updated when seeking so that future calculations
that depend on it (such as the next animation frame) will use the updated
start time based on this seek request. This allows, for example, seeking
into a running animator so that that animator will update its current fraction
to the new seeked value.
- calling reverse() on an unstarted animation would incorrectly set the initial
frame of the animation to the end value for one frame before the reverse animation
actually began.

Issue #18567716 No icons in folders in battery saving mode
Issue #18511989 Search bar flashes when icon is picked up and dropped

Change-Id: Ie30b7e797468c6ccb3d17d4fb3aba6b9849436b0