Migrate to monorepo with `higlass-schema` subpackage #313

Job	Run time
Test (3.10)	18s
Test (3.8)	19s
Test (3.9)	18s
JavaScript / Typecheck	9s
Lint	16s
Test (3.11)	16s
JS viewconf validation with generated JSON Schema	19s
JavaScript / Lint	6s
Release	0s
	2m 1s

Provide feedback