integrate SolveBio ClinVar into the collapsed result set and variant sum...

Adds a requirement for the SolveBio Python client, which contains a small wrapper for Django apps. The Django module allows SolveBio datasets to be locally aliased to avoid hard-coding dataset versions into the code. The ClinVar query is integrated into the variant API resource and filters ClinVar by chromosomal position, gene symbol, and HGVS notation.

Dataset aliases can be set in a Django setting (`SOLVEBIO_DATASETS`) and via the Django Admin (see below). The Django setting overrides the values in the database.

Signed-off-by: David Caplan <dcaplan@gmail.com>