Legacy support for multi and search routes

[alancleary]

The search route should redirect to a genes route with the single gene-source pair as the target. Since the multi route doesn't require a source, it should redirect to the new search route, which, assuming the genes entered exist in one or more of the sources listed in the config, should redirect to the new genes route once each gene's source has been resolved.

[alancleary]

Implemented in commit f441f14.

Note: the multi route actually redirects to the unified gene route (instead of a search as originally described) with every gene added to every source's matrix parameter list. This provides the same functionality as the deprecated multi route but is more verbose.