Remove the dialog that asks whether to save the draft or not and save
the draft automatically when there are changes in the composer. After
saving it show a snackbar that the draft has been saved and offer an
option to move the draft to trash from the snackbar.
MAILAND-2832
Changed the way in which the conversations are loaded from the user's perspective:
- show spinner until the whole conversation is loaded (in order to avoid showing only some
messages that have already been cached in memory),
- show the subject while the data is still loading for a better user experience
Additionally did a small cleanup of the MessageDetailsViewModelTest class.
MAILAND-2334