Add missing rejection handling for Promises (#7008)

* Add eslint-plugin-promise to detect uncaught rejections

* Move alert generation for errors to actions/alert

* Add missing rejection handling for Promises

* Use catch() instead of onReject on then()

Then it will catches rejection from onFulfilled. This detection can be
disabled by `allowThen` option, though.

package.json

@@ -129,6 +129,7 @@
     "eslint": "^4.15.0",
     "eslint-plugin-import": "^2.8.0",
     "eslint-plugin-jsx-a11y": "^5.1.1",
+    "eslint-plugin-promise": "^3.7.0",
     "eslint-plugin-react": "^7.5.1",
     "jest": "^21.2.1",
     "raf": "^3.4.0",