loci: replace validator with a stub

The negative unit tests are commented out since the stub validator doesn't do
anything.
loci: generate validator class hierachies

Includes object length checks. Does not validate lists yet.
loci: validate fixed-offset non-field-length lists

This is enough to pass all the existing unit tests.
loci: read and validate field-length members
loci: validate lists that use field-length members
loci: add TODOs to validator
BSN Image Desc Stats Req, Reply
Merge into master from pull request #252:
Fix bsn_vport subtype and add l2gre vport (https://github.com/floodlight/loxigen/pull/252)
Merge into master from pull request #251:
BSN Image Desc Stats Req, Reply (https://github.com/floodlight/loxigen/pull/251)
add util function for multiple pkt in reasons
add java doc
Merge into master from pull request #254:
add util function for multiple pkt in reasons (https://github.com/floodlight/loxigen/pull/254)
loci: remove unused validator import
Merge into master from pull request #245:
Rewrite LOCI validator (https://github.com/floodlight/loxigen/pull/245)
loci: fix compiler warning due to large constant
Merge into master from pull request #256:
loci: fix compiler warning due to large constant (https://github.com/floodlight/loxigen/pull/256)
loci: OF_HEADER is a message

It's the base class for all messages.
Merge into master from pull request #257:
loci: OF_HEADER is a message (https://github.com/floodlight/loxigen/pull/257)
java_gen: introduced HashValue type

This is a contract for types that support bit-wise operations
to support calculating and manipulating hash values.
java_gen: implement HashValue protocol