add features support for Genbank proxy parser

- add parent sequence parsing into `ProteinSequence`
- `GenbankProxySequenceReader`: add paragraph - key not started with slash character. It is added to features collection
- `FeatureDbReferenceInfo`: `DBReferenceInfo` with `Feature` implementation. In GenbankProxySequenceReader it allows to add DBReferenceInfo into children Features of the paragraph Feature