Large Gator queries timeout or return emtpy tables

It's not yet clear whether the empty table return is a cache issue (following a timeout an empty response is cached), or due to a redirect of queries to the background after ~5 mins.

Switching to TAP will resolve this bug, yet I feel it's useful to make a note about it (private/authenticated datasets should still be served through Gator).

Thanks @jkrick for reporting this issue.