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.

This commit splits the policy checks we do on node operations into
"read" checks and "write" checks, so that we can enforce different kind
of policies based on the state of a node (i.e. published or not).

This commit refactors the `NodeNodeCategory` so that we create a better
hierarchy to account for node publication, including all the policies it
might have.

Now this query accounts correctly for recursive children.

It also:

* Adds basic publish/unpublish works
* Add Move API tests scaffolding

This commit splits the old `NodeAPIEndpoint` type into three;

* `NodeAPIEndpoint`, which will also contain the freeze endpoint;
* `AnnuaireAPIEndpoint`, which is the plain old node API without extra
  features;
* `CorpusAPIEndpoint`, which will also contain the publishin endpoint.

This split ensures that we don't add endpoints which do not belong to
all three categories, like before.

Furthermore this adds a public nodes SQL queries.
It also adds tests for getUserRootPublicNode