Some clean-up of divider code in preparation for bugfixes

Made an actual class for the imecontroller in divider to
prepare for some more complicated interactions. Also consolidated
the minimize/resizability update logic for the same reason.

Bug: 150781668
Test: no change. things should work and tests pass
Change-Id: I03ca72ebd7a4b635cb91d78c18c2187b6966e514