Made image messages display externally in the layout

Previously image messages were embedded in the
messaging list instead of at the root.
Also rendering the images slightly differently such that
they don't always use the aspect ratio but can scale

Bug: 150905003
Test: add messaging layout with image, observe nice display
Change-Id: Iba25a1f81d77b58bfccbe2f9b8dfc502fdf8bdd4