Patching Part 2: Manifests

Converts everything (except for parts of plUruLauncher) over to a rewritten pl[Age]Manifest. This moves legacy manifest reading out of the net-trans code and into the manifest code. Manifest writing is currently unimplemented because there is no use case for it. This will be added later.

This changeset is independent of #277 to facilitate review. Future work will depend on both of these changesets.