- removed all old datalad-concepts 'prefixes', replaced with latest ones (also in 'emit_prefixes')
- add latest datalad-concepts schema 'imports'
- remove 'YYYY' and 'YYYYMM' types
- changed all ranges of date-related slots to 'W3CISO8601'
- changed 'is_a: FlatThing' to 'is_a: Thing'
- added PROV mixins to relevant classes
- removed all 'sh:order' annotations