Refactor FragmentTuner to ActivityConfig.

* Move model listener that opens drawer to ActionHandler.
* Move showChooserForDoc() to ActionHandler.
* Statically initialize ActionHandler.
* Isolate OnDragListener to FilesActivity only.

Bug: 28315278
Change-Id: I760c8411922fca827fd08c115bd2590ab671c380
20 files changed