- Add a send file button in conversation view
- Add new message types in chat view with buttons to control file
  transfer interactions (accept, cancel, status, etc.)
- When receiving a file, a dialog is presented to chose a location.
  It is meant to be replaced by a settable default location.
- An animation is displayed during transfer. It will be replaced by a
  progress bar when LRC side implemented.

Change-Id: I2ea0210823d697f4ada75a33b720d63288b36983
Reviewed-by: Olivier Soldano <olivier.soldano@savoirfairelinux.com>