Reorganize OPF schema

Removed special nimas module in favor of making the whole thing a
special nimas module. NIMAS is different enough from DAISY that it's
futile to try to cover both.
NIMAS validator schema update

Fixes https://code.google.com/p/daisy-pipeline/issues/detail?id=341
NIMAS-specific schema adjustments

Some educated guesses, based on discussions with APH. I am waiting for
confirmation from them but I think this will be in line with their
needs. I'm submitting it now because I'm going to be out of office for
the next 2 weeks and I know we have a release coming up.
NIMAS validator minor updates

Removed a debug statement

Removed NCX requirement from OPF schema
Merge pull request #16 from daisy-consortium/aph-feedback

Aph feedback