Start adding login and some HTML templates (UI app)

This is still work in progress, so that you know what I'm working on.

This introduces user login and logout, as well as the initial structure for the UI.

There are some things that have been copied over from ``deploystream`` without post-processing: I need to review the whole bootstrap/less code, as I was planning to use Bootstrap3 but the whole customisation we had was based on Bootstrap2 (and compression was done offline in flask whereas here we can use django-compressor).