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.

I know this patch contains a breaking change (public method `getAliases` renamed to `getAliasGroups`). Not sure if this requires increasing the version number. Probably yes.

Also this is not tested yet. It probably should.