Use a new system for constructing fragments so they can be swapped
out in place maintaining state. This will allow easier integration
with plugin lifecycle as parents who have child plugin fragments
can depend on the class existing and won't have to listen to
the lifecycle.
Test: runtest systemui
Change-Id: I517f4ce3d114abd49b1b5baca388d19e929b8f90
20ff3f9255