Re #2, take avatar pictures

copy of https://github.com/codepo8/interaction-cam/
Re #2 Avatars (from Camera)

Known issues:
- image stored as data string, not filename
- removed 'avatar upload' button from addon prefs pane
- image is 'flipped'
- bad styling
- when should this open?  Right now, it's every startup
Merge branch 'master' of https://github.com/mozilla/hotdish