Complete copyright notices for web interface; change footer to link to them.

The original copyright notice found in the footer was not accurate as it
included only one of the many copyright holders in this project. This change
creates an "about" page, which currently contains just the copyright and
license information. It links to repository for additional potential copyright
holders not listed on the about page.

Unlisted contributors are mentioned in template comments.

Html links for Kallithea is fixed and we link to Conservancy.

Display of version information in the footer is improved.