CIF data model no longer includes '_' at start of category names

src/apps/cif2bcif/converter.ts

src/mol-io/reader/_spec/cif.spec.ts

src/mol-io/reader/cif/binary/parser.ts

src/mol-io/reader/cif/data-model.ts

src/mol-io/reader/cif/schema.ts

src/mol-io/reader/cif/schema/utils.ts

src/mol-io/reader/cif/text/parser.ts

src/perf-tests/structure.ts