updated default value for Script and added mock-up for language-selector

src/apps/viewer/app.ts

src/extensions/language-select/index.ts

src/extensions/language-select/ui.tsx

src/mol-plugin-state/helpers/structure-component.ts

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

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

src/mol-script/script.ts