[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.

addressbook
basket
blog
book
calendar
comment
company
email
file
folder
i18ncontent
keyword
link
mailinglist
person
tag
timeseries
vcsfile