Resolve "Create API to get all active background jobs"
In preparation of a UI that displays the user's job in the settings page, the key under which Job IDs are stored in Redis is renamed.
All job IDs are stored under the user's ID instead of the bucket ID as key. Like this, it is much easier to get all jobs for a user. There is also more information stored alongside the celery ID (timestamp, path, protocol, bucket id)
Closes #46 (closed)
Needs to be merged after !59 (merged)