[LoginForm] refactor to ease other implementation
An Abstract BaseLoginForm is created. It is intended to be used by cubes who
want to implement new login form. It gather common login form elements in
particular the form action.
This will ease redefinition of this form action in later commit.
Whats new in CubicWeb 3.15
==========================
API changes
-----------
* The base registry implementation has been moved to a new
`logilab.common.registry` module (see #1916014). This includes code from :
* `cubicweb.vreg` (the whole things that was in there)
* `cw.appobject` (base selectors and all).
In the process, some renaming was done:
* the top level registry is now `RegistryStore` (was `VRegistry`), but that
should not impact cubicweb client code ;
* former selectors functions are now known as "predicate", though you still use
predicates to build an object'selector ;
* for consistency, the `objectify_selector` decoraror has hence be renamed to
`objectify_predicate` ;
* on the CubicWeb side, the `selectors` module has been renamed to
`predicates`.
Debugging refactoring dropped the more need for the `lltrace` decorator.
There should be full backward compat with proper deprecation warnings.
Notice the `yes` predicate and `objectify_predicate` decorator, as well as the
`traced_selection` function should now be imported from the
`logilab.common.registry` module.
Unintrusive API changes
-----------------------
* new 'ldapfeed' source type, designed to replace 'ldapuser' source with
data-feed (i.e. copy based) source ideas.
RQL
---
User interface changes
----------------------
Configuration
-------------
Base schema changes
-------------------
Email address 'read' permission is now more restrictive: only managers and
users to which an address belong may see them. Application that wish other
settings should set them explicitly.