Docs: Rename Query API to focus on building URLs instead of "querying"

[dmsnell]

When I look at the docs and see "Query API" I think of something trying to search through things or form a query, but this is actually where you should go to learn how to build a URL to load the Playground into specific configurations.

Something like "URL Query API" or "URL Search and Hash API" or "Playground URLs" or even "URL API" could potentially improve the match between what it's doing and what it's called.