Make module able to work without single use link

Because of peculiarities with one of the networks our users are on, we cannot use single-use links on our site. I think the module could be made to work without the link by breaking up the !site_url token into smaller pieces and providing an input form which would be displayed for the user to input the hash value if it is not provided in the url.

I'll hack on it some when time permits, but wanted to throw out the idea for comment.