Fixed #321: One judgment keyword model class for all court types

Probably currently cleaner solution would be to move this method to the `pl.edu.icm.saos.api.single.judgment.mapping.JudgmentMapper ` and  field
`pl.edu.icm.saos.api.single.judgment.data.representation.CommonCourtJudgmentData#keywords` ->
`pl.edu.icm.saos.api.single.judgment.data.representation.JudgmentData`