Maybe this will fix notifications for job finish

It might be that notifications get mixed up when running parallel
test (as they use the same port)

More import refactoring

[TESTED] Worker Tested and README info to create the database, launching and configuring it. Thank your Przemysław for this nice upgrade.

Also, use genericArbitrary in Instances, this simplifies things

Also, some import refactoring

This function extracts the Node.Update logic for `publish_node` into a
separate function, so that we can use it in a `POST` request, i.e. a new
endpoint for publishing nodes.

Previously there was no symmetry in the name of the share endpoint,
which is meant to be used to generate a publicly-accessible URL to view
a node, and the previously-called "unpulish" endpoint.

The problem is that now the "unpublish" name would clash with the dual
of publishing a node. To avoid the problem, this commit renames the old
"unpublish" endpoint to be "unshare", so that now it's clear that is the
inverse operation of "share".

This allows the frontend to correctly display a different icon in case a
node has been published with edits enabled or not.

Previous to this commit, `get_user_root_node_folder` would fail with
a `UserHasTooManyRoots` in case this was called on a tree which had
more than one "public" folder.

We fix this by taking the oldest available node, which will always
correspond to the notion of "root", being the first ever created.