mod_authentication: Refactor twitter/facebook logon and signup code.

Now uses a popupwindow for the authentication.
Twitter and Facebook settings are combined in the admin underneat the 'Auth' menu.
Authenticated users are immediately signed up, no extra checks.
mod_base: do not redirect if redirect id is set to undefined
mod_base: in do_popupwindow use e.preventDefault() to play nice with multiple click event listeners.
mod_mqtt: fix js error in for loops.
core: the {% script %} tag has now arguments.