feat(preferences): frontend logic for user preferences
fix(preferences): improve the code
fix(styles): move medium editor styles to superdesk
fix(styles): authoring dashboard fix

+ center opened articles
+ remove plus button from opened articles
fix(styles): improve assignee box styling

improve assingee box
feat(tasks): Implemented picking tasks.

SD-730
Merge remote-tracking branch 'nikola/ui-update' into devel
Merge remote-tracking branch 'nikola/user-preferences' into devel