Schema loading should be constrained by a set of schemas

[stroomdev66]

The schema filter can be constrained by a schema namespace, system id or schema group but this limitation only applies to the outermost schema and not others that could be loaded by the LSResourceResolver. The schema filter ought to allow a user to provide a list of schemas that could be used in the context of the schema filter to provide tighter control.

[stroomdev66]

Issue #358 provided some changes to constrain the LSResourceResolver but more needs to be done.