Fix mosaic quad info/contribution

[joferkington]

Mosaic quad information retrieval (i.e. mosaics quad-info and mosaics contribution) is currently broken. For example:

$ planet mosaics quad-info basemap_medres_weekly_permian_20180917_20180923 446-1201
Error: InvalidAPIKey: {"message":"Insufficient Privileges"}

ClientV1.get_quad_by_id currently constructs the url it requests by naively appending paths to the mosaic's _links.self. However, mosaic url returned by the api has the user's api key included as a parameter. This results in a url with the quad's path as part of the api_key parameter, resulting in the 403 response.

E.g. planet mosaics quad-info basemap_medres_weekly_permian_20180917_20180923 446-1201
actually requests https://api.planet.com/basemaps/v1/mosaics/1e9ae02c-64b7-428d-bbcd-7df3f9a94f14?api_key=FOOBAR/quads/446-1201

This PR fixes the issue by constructing the quad url based on the mosaic's id and the quad endpoint.

[joferkington]

Note that test failures are unrelated to this PR. They're because additional item types have been added to the api, and the test checks against a fixed list. (Specifically, SkySatCollect and the various MODIS item types are not in the fixed list.)