GitLab

• JSON validation in now performed against json-schemas which gives a standard way of handling this.
• All previous validation moved to new setup (useful_links field & TaggedItem in particular)
• Tags handling slightly updated (schemas are now hardcoded in the app and not stored in db)
• A bit of documentation added

• Bumped backend image to version 0.2.1 with new python packages requirements

Fixes #112 (closed) Mentions #113 (closed) #57 (closed)