pyloxi: support OXM member in set-field actions

The C backend needs more work to support of_oxm_t, so I've added a hack so it
can keep using of_octets_t.

Also added several set-field action testcases.
pyloxi: factor out loxi.generic_util.pad_to
pyloxi: slightly generalize alignment

The _pack and _unpack templates should not be matching on particular class
names. Move the decision up a few levels to codegen.
Merge into master from pull request #36:
implement OF 1.3 set-field actions in pyloxi (https://github.com/floodlight/loxigen/pull/36)
java_loxi: big refactoring and clean-up
java_gen/pre-written: fix exceptions
java_gen/U64: fix bug with treatment of usigned long values > Long.MAX_VALUE
java_gen: add Dummy OFFlowMod
java_gen/java_model: do not memoize enum.get_all_values (arg not hashable)
java_gen/java_type: support $version for string version of readOp/WriteOp
java-Gen/of_class: fix typo in reader
java_gen: change to maven build, remove lib directory
Make: add maven build for java
Merge branch 'master' of github.com:floodlight/loxigen
Merge branch 'java-work-andi'