Fix zoom transition to prevent cell frame warnings.

It never made sense for the presentedView frame to
change when setting up for zooming out. This
caused warnings for a while about the cell frame
being too big.
Rename local view controllers in zoom animation method.

'source' and 'presented' are misnomers for to and
from view controllers, since source and presented
never change regarding to a transition, but to and
from are dependent on transition direction.