feat!: major API and routing changes

[AlexCLeduc]

Working towards #58, won't get everything done,

Definitely will get done:

• Add a ton of tests
• Decouple classes from names and routes
• Allow request access in search/get items
• split up get_items into search and get_values_for_keys
• Add authorization hook
• Update translations
  • supports string substitution e.g. showing %(x)s of %(y)s
• Better pagination?
  • better message (e.g. showing x of y)
  • encouraged use of max results
  • efficient slicing/counting of querysets
• Update docs

Less certain about getting these this release...

• Exposing a cleaner JS API
• An API to augment hx-vals/params to include other things on the request
  • i.e. allow the search function to take into account other form fields