Add a XmlStream with privacy list invisibility
Add a XmlStream with privacy list invisibility

This class allows you to run a test against a server which Gabble
believes supports privacy list-based invisibilty without any further
modifications to the test. This will allow us to check that invisibility
support doesn't break other functionality.

We already have a Xep0186Stream which claims to support another dialect
of invisibility that Gabble understands. It doesn't actually let you
become invisible, but this shouldn't matter for non-invisibility-related
tests.

jku/telepathy-gabble,jku/telepathy-gabble,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble,mlundblad/telepathy-gabble,mlundblad/telepathy-gabble,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble,jku/telepathy-gabble,mlundblad/telepathy-gabble