allow specifying path for quilt storage

[knaaptime]

the default storage path works fine for most applications but fails on travis. This allows a user to specify a download location where the quilt package, which should make it easier to solve issues like these https://travis-ci.org/knaaptime/geosnap/jobs/653970124?utm_medium=notification&utm_source=email

[knaaptime]

🙄 I guess I'll revert this.

the issue is we need to provide a path to the NLCD raster. Installing the quilt package ensures that the raster is downloaded to the system, but quilt cant seem to find the path--i'm not sure why.

Nothing is actually broken, so i can revert this and handle the tests differently, but this also means I'd need to write some additional code for, e.g. https://github.com/spatialucr/geosnap-guide because we test those notebooks on travis.

ideally i'd like to avoid that, and only have the "canonical" example in those notebooks, but whatever

notebook no longer executes directly