Add function to suggest mappings to CL terms based on lexical matches

[dosumis]

OAK has lexmap function(s) that can fuzzy match strings to ontology terms based on labels/synonyms. Pandasaurus enrichment allows us to narrow down potential mappings for cell types to branch of CL.

New function: use author cell type names to find candidate lexical mappings from among the subclasses of the CL term. Investigate using LEXMAP for this. For an MVP just use direct annotation (subcluster_of entries in the co-annotation table). IN future we may extend this to use cell sets)