MAINT: rework ipac.irsa.ibe to use the VO backends

[bsipocz]

The server side backend has changed since the module was implanted, and a lot if not all the functionality is now available via the standard VO endpoints. So we need to cleanup the module and add documentation of how to use IRSA to get access to the same results.

Practically this is about to write documentation and thus be able to deprecate and the remove the standalone module.