[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.

[request] gather all base_url logic in a single place (closes #2200756) * Handle ``https base-url`` in the core code: ``./req.py`` and ``web/request.py`` * Remove custom ``base_url`` handling if web request

[http] drop use-request-subdomain feature (closes #2251986) This feature do not have any user nowaday and lays in the path to WSGI.