Revisions: Combine our tooltip and from/to templates into one generic template

We had three copies of essentially the same template. Now just one, with minor logic inside.

Also fixes a bug where tooltip.revision was being initially set to a diff instead of a revision.

For trunk. See #24804.

git-svn-id: https://core.svn.wordpress.org/trunk@24814 1a063a9b-81f0-0310-95a4-ce76da25c4cd