Isolate Menu/Action management into dedicated manager classes.

We are now also returning fragmentTuner at the activity level, so that
directoryFragment does not have to do a .pick() logic depending on the
activity type. Rather, the logic lies within the activity itself.

Bug: 24416336
Change-Id: Idb200864f6c9468b9193781f6ac505b557ffbce9
(cherry picked from commit bc330a4bf53c3a766292097d1815b9abd469a945)