templates: Link "Imprint" to /imprint

We don't use this config option anymore
controllers: Added AboutController
README: Moved authors list to AUTHORS file

.. and added the missing developers and translators according to the
git history. Some more from launchpad might still be missing.
controllers: Added /about/team page that shows the AUTHORS file contents
templates/base-page: Changed team link to /about/team
controllers: Moved imprint page to /about/imprint
controllers: Use generic page template for Imprint page
controllers/error: Use generic page template for error pages
Merge pull request #48 from Turbo87/authors

Added AUTHORS file and web view