LB-8: Tageswoche livedesk:mobile issues (IOS)

fixed default theme.
revert LB-56 : Add the source key to the Source(superdesk-source) model
Made ffmpeg the default thumbnail generator

We still have issues with GraphicsMagick not working on different systems
LB-306 : Change names of users and live blog in default demo database
LB-306 : Change names of users and live blog in default demo database
LB-349: Share functionality does not work on default embed templates

Embed now has default theme.
LB-433 : Twitter search: urls in a tweet

Done
NR-962 : Add article not working

internationalization elements