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
Merge remote-tracking branch 'sourcefabric/liveblog-13'

Conflicts:
	plugins/livedesk-embed/gui-resources/index.html
	plugins/livedesk-embed/gui-themes/themes/default.min.js
	plugins/livedesk-embed/gui-themes/themes/default/item/base.dust
	plugins/livedesk-embed/gui-themes/themes/default/item/source/flickr.dust
	plugins/livedesk-embed/gui-themes/themes/default/item/source/google.dust
	plugins/livedesk-embed/gui-themes/themes/default/item/source/instagram.dust
	plugins/livedesk-embed/gui-themes/themes/default/item/source/soundcloud.dust
	plugins/livedesk-embed/gui-themes/themes/default/item/source/twitter.dust
	plugins/livedesk-embed/gui-themes/themes/default/item/source/youtube.dust
	plugins/livedesk-embed/gui-themes/themes/default/livedesk.css
	plugins/livedesk-embed/gui-themes/themes/stt.js
	plugins/livedesk-embed/livedesk_embed.egg-info/SOURCES.txt
	plugins/livedesk/__plugin__/livedesk/blogs.csv
	plugins/livedesk/__plugin__/livedesk/populate.py
	plugins/livedesk/__plugin__/livedesk/populate_default_data.py
	plugins/livedesk/__plugin__/livedesk/posts.csv
	plugins/livedesk/gui-resources/scripts/js/providers/twitter.js
	plugins/media-archive/__plugin__/media_archive/service.py
	plugins/superdesk-security/__plugin__/superdesk_security/populate.py
Merge remote-tracking branch 'sourcefabric/master' into devel