Add Support for Built-In Colophon Page

[chipbennett]

Add support for a built-in colophon page, with appropriate filters/hooks for theme and plugin developers to provide an optional credit/link in the colophon.

This solution would provide a standardized location for such credits/links, would encourage users to allow such links, and would (hopefully) alleviate current concerns regarding appropriate means (and amount) of crediting/linking plugin/theme developers.

[nacin]

-1, this should be reserved for a plugin.

[scribu]

-1, there already are standard, optional, credit links on the plugin page.