openflow_input: add bsn_egr_port_group_id extension
Merge into master from pull request #221:
java_gen: add documentation to string-parsing 'of' methods (https://github.com/floodlight/loxigen/pull/221)
java_gen: support of_oxm_bsn_egr_port_group_id

It's basically a class-id, so using that type.
Merge into master from pull request #222:
openflow_input: add bsn_egr_port_group_id extension (https://github.com/floodlight/loxigen/pull/222)
loci: fix bug in new wire type parsers

Using the unified class's discriminator was incorrect because the discriminator
can change offset and length between OpenFlow versions.

Also added tests that would have caught this bug.
Merge into master from pull request #223:
loci: fix bug in new wire type parsers (https://github.com/floodlight/loxigen/pull/223)
java_gen: make of_aggregate_stats_request.out_group type OFGroup