wip 2.0 rewrite: handle paginated responses
Better pagination handling, searching, users.
Add more unauthenticated objects and break the client into modules.
Add initial support for OAuth requests.
Make URLs configurable per-client.
Fix headers not being supplied correctly.
Rename paginated list classes for clarity.
Add artist groups.
Fix missing import.
wip: start on manipulation of remote objects
Add helpers for metaprogrammatically adding fetched properties.
Allow certain Fetched properties to be set.
Replace reundant property declarations with @fetches decorator.
Use POST instead of PATCH for now.
Refresh the object after saving.
Remove unneeded default when constructing Listing price.

All Listings have prices, and if there was one that didn't,
an empty dict wouldn't be a valid Price anyway.
Add order management.
Stylistic improvements to cache lookup logic.
Enable modification of WantlistItem properties.
Replace `fetches` decorator with metaclass.