Fix model interfaces

The important commits here are about fixing references to nonexistent arguments and schemata.

- https://github.com/rackerlabs/otter/commit/9696a7a4fe2373b787d7dd99546af611bf041657
- https://github.com/rackerlabs/otter/commit/d6c653ce37becd805da09959ae1d828a2e1038af

Everything else is just about making stuff a bit nicer :)