ENH: adding extra, non-spatial filter keyword to query_region methods

[bsipocz]

E.g. for IRSA, the query_region method is building up an ADQL query under the hood. So, especially for the All-Sky spatial use-case it would be useful to be able to specify other filtering criteria.

This maybe useful for other modules, too, at least for the ones using TAP under the hood for their query_region.