curationLevel -> assertionMethod

Kept in line with the dataset description guidelines
Removed double drop of mappingSetTable
Added new ChemicalRegistry URI pattern
Merge branch 'develop' of git@github.com:openphacts/BridgeDb.git into develop
Merge branch 'develop' into byGraph
Merge branch 'byGraph' into Christian
Merge branch 'Christian' into svnMerge