Add convenience methods to Fingerprint

This covers most of the wishes I had in my email.

One thing I did not implemented are hasLabel, hasDescription and
hasAliasGroup methods, similar to the remove... methods.
Language magic removed and tests added
Moved setAliases to setAliasGroups rename to other pull request
Merge pull request #59 from wmde/fingerprint-convenience

Add convenience methods to Fingerprint