Clean up Data class.
Clean up TYpe.
Clean up Scheme.
Remove some warning.
Clean up data conversion exceptions.
Clean up Cryptography and CryptographyBuilder.
Satisfy CheckSyle for all classes in the `dssb.cryptography` package.
Add class segment divider.
Reorganize the source folders so that we can later package them
separatedly.
Refactor the data type, JavaDoc and add jUnit test.
Same as before.
Satisfy checkstyle.
Satisfy checkstyle.