message: packages/cli: add missing theme dep to app template
diff: "@material-ui/icons": "^4.9.1",
  "@backstage/cli": "^{{version}}",
  "@backstage/core": "^{{version}}",
  + "@backstage/theme": "^{{version}}",
  "@testing-library/jest-dom": "^4.2.4",
  "@testing-library/react": "^9.3.2",
  "@testing-library/user-event": "^7.1.2",
  