Query parameter for table/catalogue pre-selection

[molinaro-m]

There are many cases where a unique conesearch service engine serves multiple catalogues in the backend. The usual solution uses an extra query argument in the ConeSearch base_url to split the registration in multiple ConeSearch services.

In the process of moving to a solution without extra arguments in the base_url (see issue #31 ) a way could be formalising an optional query parameter, e.g. CATALOG, to achieve the same result, thus preparing for a smoother transition towards a no-extra-args specification.

This parameter has the same drawbacks in terms of registration and w.r.t. clients than the TIME one.