GitLab

Small usability fixes for the execution inspect page
Move all the database access in the state package
Remove image management, it is too slow to download images before while the user waits the the ZApp to start
Make several thread loops more robust in case of uncaught exceptions

Open enpoint links in new windows and prevent a race condition when a new execution is added to the scheduler queue

If activated, docker will be configured to send service logs to the zoe master, who will save them to disk. Then they can be streamed via the command line or the web interface.

Expose container-level error messages to the user through the service error_message field
Closes #31