Big pull request - mainly to get the loxi_ir changes in

Reviewer: @rlane

Apologies for a relatively unorganized big pull request. This mainly has a lot of changes to java_gen and a few changes that affect other modules/the input:
 * support for OFDescriminatorMembers for abstrat classes
 * support for wire_type parameters for enums
 * support for align parameters for classes.

@rlane: Mainly focus on the frontend changes. The java stuff is just coming together.