replace deprecated cubicweb.common.selectors by its new module path (cubicweb.selectors)

move EProperty management views into eproperties.py

should add relation_possible selector only if require_permission is in the schema

missing super call

remove all accepts = ('Foo',) declaration and use __selectors__ = implements('Foo') instead

removing explicit access to im_func, this is not necessary anymore

allow selectors to be a single element instead of tuples (this is the first step towards removing the metaclass)

registerer cleanup

fix imports

fix initializers