Rename "citation" to "cite" to better match KG fields

Included bigbrain extension regions for Julich-Brain 2.9

Introduced map_type for volume datasets in parcellations (set to 'continuous' for probability maps and difumo maps, otherwise 'labelled')

Unified volumeSrc and originDataset fields with heterogeneous substructure among parcellations, spaces and regions into a unified flat structure "datasets". Decoding the different forms is now implemented in siibra at a single point by common parent class "SemanticConcept".

First version of Julich-Brain 2.9 and freesurfer representation of its  maximum probability map

Set julich-brain 2.7.3 to beta.

Including probability maps for bundles for Version 0.1a3

julich-brain 273 included