Boot custom CSS, and put some base, standard css in its place.
Shame I did not start with fresh Bootstrap4, but oh well.
Some more templates could be made to make this less messy, which would
be good.
* Simple form input fields now use TakeFlight styling
* Styles the form widgets as per the styles in our CSS
* Styling of TextArea now matches the remaining input types
* Adds is_last modifier to navigation dropdown
* Adds admin for talk, tutorial, and miniconf proposals
* Adds an RSS feed
* Adds a link to the RSS page
* Unbreaks the old news index page
* Adds never_cache to the login page, removes the never cache middleware from the settings
