Add GT metadata to service.

[VolkerHartmann]

No description provided.

[kba]

Blocked by OCR-D/spec#85 OCR-D/spec#86

[EEngl52]

@kba is this still relevant?

[kba]

Since we lack the resources to deploy the KIT Data Manager on our own and @VolkerHartmann has left the project, I think not.

[VolkerHartmann]

There is already GT metadata linked to the data. The issue was created to find the 'most important' ones especially for creating filters due to them and is related to OCR-D/spec#85. The filters available right now: Semantic Labes, Classification, language and id.