Java Bindings: use cached QNames

Each generated class carries a QNAME element inside it, which can be used when interacting with the data in binding independent form.

The code looks like this:

public static final QName QNAME = org.opendaylight.yangtools.yang.common.QName.create("urn:opendaylight:params:xml:ns:yang:bgp-rib","2013-09-25","tables");;

With advent of cached QName/QNameModule references, we can actually use these to pre-populate cache, such that most of our comparisons end up referencing the same QNameModule/QName object, thus speeding things up.