Replace the buggy schema parser by one based in GTXML and EMF-XSD

At the time the complex-features branch was created, the were no an existing parser to get {{FeatureType}}s out of a community schema in XML Schema files, so we used a quick, dirty and ugly one with lots of limitations.
Now the scenario is completely different, GTXML can be used together with EMF, as it fits perfectly as FeatureType metadata so we don't lose a single bit of the actual community schema we're working with, since the emf type definition object in the schema can be stored as a "userData" property for each FeatureType, as well as the emf element declaration for each AttributeDescriptor.

This information could well serve at a later step to actually be able to creating valid GML documents for the community schema by the use of a schema assisted encoder.
So we just have thrown away the old and ugly schema parser, which won't work anyway due to the FM API shift, in favor of a new, emf based one, that reuses the GML to FeatureType bindings in GeoTools.

Note that since these bindings exists for the current GeoTools Feature Model, we're again using adapters to go from geotools FeatureTypes to ISO FeatureTypes. This situation is temporary though, and should last only until the ISO Feature model is adopted, in which case the GML bindings are going to be ISO FeatureTypes by them selves.