…git-lfs.

Up to this point, all data dependencies have been github cov-lineages repositories.  The cache file in pangolin-assignment exceeded the github file size limit so we changed the pangolin-assignment repository to use git-lfs.  Thanks @pvanheus for pointing out that github has storage and bandwidth quotas for Git LFS usage, and that by default the pangolin-assignment release tarball from github does not include the cache file; it can be added to the release tarball, but will count further against the storage and bandwidth quotas.
Since the cache file is generated at UCSC which has ample web server storage and bandwidth, this adds a new mechanism to search for the latest versioned tarball in a web directory (instead of querying the github API), compare its version to the locally installed package if present (using the same pip/__init__.py __version__ mechanism), and install the tarball from the web directory (instead of github).
Note: currently the URL for pangolin-assignment uses the hgdownload-test server; this will need to be changed to hgwdownload after some testing and before release.

…ssignment versions. There may be patch releases that make sense for pangolin-data but not pangolin-assignment (e.g. pangoLEARN patch update), and the suggestion to run --update-data is not helpful because that's how the versions came to be installed in the first place.

Also fix option name typo in github query exception message.