Template hierarchy

Here we massage the template and css structure into something a bit more understandable and extensible. 

The previous structure was done in a pretty add-hoc fashion, just trying to get a few pages up and running. With this change we try to segment our html and css between the topbar-menu based homepages and the sidebar-menu based account pages.

The login page is still a bit ad-hoc (it doesn't have a menu bar, so it inherits from base.html and defines its own css), but that can be better organized later. For now, it looks nice and is simple.