Added TestOriginConverter.

- Fixed a few issues in OriginConverter, including CanConvert not checking
  types correctly and made origin names internal.
Added tests for LevelConverter.

- Added TestConverter base class for common tests and modified
  TestLevelConverter and TestOriginConverter to use it.
- Added NCrunch files to .gitignore.
- Added InvalidSerializationException to abstract serialization errors and
  changed LevelConverter and OriginConverter to use it.
- Fixed a few issues in LevelConverter.
Moved TestSerialization from Unit to Integration tests.