feat: enum labels for spdx.schema.json (#839)

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modified the generator for the SPDX schemas, so that 
- the strings in the respective output tiles are escaped/safe now. 
- JSON enums have labels - just like in the XML has
- JSON schema version was bumped from `v1.0-...` to `v1.1-...` since we
added the feature "labels"

Author: jkowalleck