Unify how ROW_LIMIT works for all services about astroquery

[cdeil]

At the end of the IRSA Getting Started it is mentioned to use

Irsa.ROW_LIMIT = 1000

This doesn't work any more and ROW_LIMIT does not appear in the Irsa class API docs.

[keflavich]

This is definitely important; wherever possible, a row limit should be allowed. I think a global row limit, from which all others could inherit, would be useful. However, the default limit should probably be unlimited. Any further opinions on this?

[keflavich]

I'm assuming that @jdnc's PR fixes the consistency issue for all of the refactored modules, but we'll need to keep an eye on this for others, so I'll keep it open.

[keflavich]

I'm marking this as fixed now: many servers do not offer any row limitation option, which is why it is not part of the query service. If any DO support row limits, we should add it as part of astroquery.