RunQuery currently assumes a single index. To test PubMed/Wikipedia expansion, we need the ability to configure a separate expansion index from the actual index-to-be-queried.
The implementation should support:
- Configurable expansion index (e.g., pubmed), scorer (RM1, RM3) and parameters (mu, fbdocs, fbterms, lambda)
- Configurable primary index and scorer (Dirichlet)