1811 provide graphql api (#1829) * Fixme (Remove 'True') - Add GraphQL starting point to the web server. * Add GraphQL Schema. * Experiment with the graphql-api package. * Remove the graphql-api package again. * Respond with GraphQL mimics. * Add types for GraphQL mimicking. * Add example queries. * Add proof of concept database fetching. * Add Signature query resolver. * Add SignatureMorphism query resolver. * Add missing key to result JSON. * Add Serialization resolver. * Split code for conversion and retrieval of data. * Fix indentation. * Add OMS query. * Add DGraph query. * Remove commit and document from example queries. * Remove GraphQLApi constructor again. * Save libenv to database via RESTful interface. * Fix line lengths * as library name, ensure a URL containing, in case of file://, an absolute file path * correction: urls should not be treated as file path * avoid re-reading for xmi and qvt; corrected computation of full filename * strip file:// prefix for OWL parser * strip file:// prefix for QVT parser * introduced utility function tryToStripPrefix * strip file:// when writing files