fix #224 - floating admin-only logo and admin.css getting included in non-admin pages

- fix is: all admin (non-public) pages inherit from base-admin.html which defines additional theming and inherits base.html
- public stuff now inherits base.html only which doesn't define those elements

reviewers: the two files to pay attention to are base.html and base-admin.html

I hope there wasn't a more clever way of doing this but I think this is the easiest.

PyCharm made finding and replacing all the base.html a breeze.