Extract MessageListAdapter.

Change-Id: I0e441b7fff925c7703ab88ab54240c5b42d045c4
Remove Handlers from Activities.

AccountFolderList, MessageCompose and MailboxList.

Also,
- ControllerResultUiThreadWrapper now takes a Handler instead of an Activity.
  So that it can be used from a Service as well.

- ControllerResultUiThreadWrapper.getWrappee() to get the wrapped object.
  We'll eventually need this.

- I'll work on MessageList too, but the might be relatively
  large, so I'll do that in a separate CL

Change-Id: I281d88d5af1834248ec3f7463f0df3f5635149be
Merge commit '4a2615e2a587e842390e124def03e90d8772c6d1' into oxygen_1006

* commit '4a2615e2a587e842390e124def03e90d8772c6d1':
  Remove Handlers from Activities.
  Extract MessageListAdapter.