Enhance puzzle list sorting and filtering

[luxaritas]

Some of these will require backend changes, which are being tracked elsewhere. Also, some of this was already previously started by Alex in #215, though that PR needs to be revisited.

Filters

• [x] Number of states (min/max) (or, if not possible in the backend, filter for switch instead of only single)
• [x] Tags (for POTW, etc which currently relies on the cocreator "extended search", and can now use the new "tags" field)
• [x] Dedicated search box for author (using new creator_uid backend field)
• [x] Solver count (min/max)
• [x] Point count (min/max)
• [x] Length (min/max)
• [x] Folding engine

Sorts

• [x] Least solved
• [x] Longest
• [x] Most/least points

[luxaritas]

I'm actually going to explicitly not support tags - our only use case for it was covered by collections

[luxaritas]

Done in #215