[vreg] move base registry implementation to logilab.common. Closes #1916014 A new logilab.common.registry module has been created with content from * cw.vreg (the whole things that was in there) * cw.appobject (base selectors and all). In the process, we've done some renaming: * former selector functions are now known as "predicate", though you still use predicates to build an object'selector * hence `objectify_selector` decorator is now `objectify_predicate` * the top level registry is now `RegistryStore` (was `VRegistry`) Also there is no more need for the @lltrace decorator. On the CubicWeb side, the `selectors` module has been renamed to `predicates`. There should be full backward compat with proper deprecation warnings.

+
−Document: cubicweb-doc
+
−Title: CubicWeb documentation
+
−Author: Logilab
+
−Abstract: Some base documentation for CubicWeb users and developpers
+
−Section: Apps/Programming
+
−
+
−Format: HTML
+
−Index: /usr/share/doc/cubicweb-documentation/index.html
+
−Files: /usr/share/doc/cubicweb-documentation/*.html