[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.

Latest changes 
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* table of `all latest changes`_

Links below is providing useful RQL query example.

.. _all latest changes: view?rql=Any+M%2CX+WHERE+X+modification_date+M+ORDERBY+M+DESC+LIMIT+30