Add hashes to finite group interface #5556

We've computed hash values for finite groups in several contexts (the hash column of gps_groups, subgroup_hash and quotient_hash columns of gps_subgroups), but they're not visible in any way on the front end. There are several places they could go:

• Somewhere on the group/subgroup homepages
• In the Find box, so that a user can input an order and hash and see all the groups we have with that order+hash (and for orders where we can make completeness guarantees, if there's only one group with the given hash then we can just forward to the appropriate homepage).
• As an optional column in search results.

As a followup, this is a prerequisite to allowing users to type in a group description in the find box (like permutation generators or a PC presentation).