SpatialDB change API

Summary: I changed SpatialDB API so that we only specify list of indexes when we create the database. That way, whoever is querying the DB doesn't need to know the full list of indexes and their options.

Test Plan: spatial_db_test

Reviewers: yinwang

Reviewed By: yinwang

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D20571