Add a "return to mod tools" link to the mod-tool pages, based on the link that already existed on the flag-queue page. Two noteworthy cases:

1. I added it to the Reports page along with the rest, but that page produces a 500 error in my dev environment (with or without my change) so I can't test it. The error seems to be about time zones. (Of course. It's always time zones. Let's abolish them.)
2. The mod-tools page includes a link to create a new help topic. This goes to the regular "create post" page. I couldn't quite figure out how to check there for the help-specific case, so I didn't change anything there. It's probably a rare mod action, so I'm proceeding with the rest anyway.

Fixes #272.