Allow query strings for precomputed chunks URLs

Currently, neuroglancer will error out on datasets of the kind `precomputed://http://` if they contains query parameters. This is particularly annoying when serving data from Opentsack Swift's temporary URLs, since those come with signatures in the query parameters.

It seems natural to allow URLs to be derived from the base URL as usual, but also appending the query params to the string, but I haven't given too much thought on what consequences that could have.