[notification] use an InternalManager object for notifications if we have an (email, lang) tuple
The non-uniform handling of CWUser vs (email, lang) tuple has caused too
many bugs; this change mostly unifies the two code paths. Closes #3381521
usr/lib/PY_VERSION/*-packages/cubicweb/entities/
usr/lib/PY_VERSION/*-packages/cubicweb/ext/
usr/share/cubicweb/cubes/
usr/lib/PY_VERSION/*-packages/cubicweb/*.py