let non-authenticated users browse the data

[mfrasca]

we are making a read/write interface, requiring everybody to be logged in.
in reality, we should hide parts of the user interface for not logged in users, add a login/logout button, and secure the views.

• secure the non-safe api URLs,
• add a login-logout button
• identify the user interface to be protected
• use css to hide/show those parts

[mfrasca]

not css: I used the django rendering engine