transmitting files between two conversations works. no error handling and no ui on the receiving end
Major Contact Picture code cleanup

Notifications now have pseudotransparent icons, icons are generated in
the correct size.
Added ellipsis tile for large conversations

For more than 4 members in a conversation, the fourth tile now contains
an ellipsis to indicate this
Some icon tweaks

Use Roboto Light, thinner lines between tiles, slightly smaller letters
added contributors and note to xep65