Core: implement Flickr sign out

Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>
Authoring: Fix forms

Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>
ContextPanels: By default, activate all the context panels. Rename "Edition" to "Actions".

Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>