Add a "Last Rendered" view to the webapp.
The Manager now stores (in the database) which job was the last
recipient of a rendered image, and serves that to the appropriate
OpenAPI endpoint.
A new SocketIO subscription + accompanying room makes it possible for
the web interface to receive all rendered images (if they survive the
queue, which discards images when it gets too full).
When a job or task gets requeued from the web interface, its task
failure lists (i.e. the list of workers that previously failed this
task) will be cleared.
This clearing doesn't happen in other situations, e.g. when a worker
signs off and its task gets requeued, the task's failure list will
remain as-is.
A task can exist in the database but not have any log stored on disk yet.
This is now returned as `204 No Content` instead of an internal server
error.
The web interface is also adjusted to cope with this.
The add-on code was copy-pasted from other addons and used the GPL v2
license, whereas by accident the LICENSE text file had the GNU "Affero" GPL
license v3 (instead of regular GPL v3).
This is now all streamlined, and all code is licensed as "GPL v3 or later".
Furthermore, the code comments just show a SPDX License Identifier
instead of an entire license block.
