Expose more XJC attributes to generateSchema task.

Using 'src/${sourceSet.name}/xjb as default source for binding files.
Using 'src/${sourceSet.name}/xsd/catalog.dat as default catalog.
Using no default package name.

Override those settings by:
generateSchemaSource.bindings
generateSchemaSource.catalog
generateSchemaSource.packageName
Merge pull request #19 from stephanheinze/master

 Expose more XJC attributes to generateSchema task