added ShapeProvider and hooked it up in plugin

src/mol-io/reader/ply/parse_data/ply_parser.ts

src/mol-model/shape/formarts/ply/plyData_to_shape.ts

src/mol-model/shape/provider.ts

src/mol-plugin/index.ts

src/mol-plugin/state/actions/basic.ts

src/mol-plugin/state/objects.ts

src/mol-plugin/state/transforms/data.ts

src/mol-plugin/state/transforms/model.ts

src/mol-plugin/state/transforms/representation.ts

src/mol-repr/measurements/representation.ts