[repoapi] introduce a basic ClientConnection class
This is the new official way to access the repo from client side.
It still access Session object directly as the server side connection is not up
yet (and it's not up because it would have no user).
Multiple follow up commit will install compatibility with the DBAPI. This will
ease the migration from dbapi to repoapi.
ClientConnection has no user yet but later commit will use it in the whole Web
stack.
related to #2503918
What's new in CubicWeb 3.17?
============================
New functionalities
--------------------
* add a command to compare db schema and file system schema
(see `#464991 <http://www.cubicweb.org/464991>`_)
* Add CubicWebRequestBase.content with the content of the HTTP request (see #2742453)
(see `#2742453 <http://www.cubicweb.org/2742453>`_)
* Add directive bookmark to ReST rendering
(see `#2545595 <http://www.cubicweb.org/ticket/2545595>`_)
* Allow user defined final type
(see `#124342 <https://www.logilab.org/ticket/124342>`_)
API changes
-----------
* drop typed_eid() in favour of int() (see `#2742462 <http://www.cubicweb.org/2742462>`_)
* The SIOC views and adapters have been removed from CubicWeb and moved to the
`sioc` cube.
* The web page embedding views and adapters have been removed from CubicWeb and
moved to the `embed` cube.
* The email sending views and controllers have been removed from CubicWeb and
moved to the `massmailing` cube.
* ``RenderAndSendNotificationView`` is deprecated in favor of
``ActualNotificationOp`` the new operation use the more efficient *data*
idiom.
* Looping task can now have a interval <= ``0``. Negative interval disable the
looping task entirely.
* We now serve html instead of xhtml.
(see `#2065651 <http://www.cubicweb.org/ticket/2065651>`_)
Deprecation
---------------------
* ``ldapuser`` have been deprecated. It'll be fully dropped in the next
version. If you are still using ldapuser switch to ``ldapfeed`` **NOW**!
* ``hijack_user`` have been deprecated. It will be dropped soon.
Deprecated Code Drops
----------------------
* The progress views and adapters have been removed from CubicWeb. These
classes were deprecated since 3.14.0. They are still available in the
`iprogress` cube.
* API deprecated since 3.7 have been dropped.