migrate core to emotion

packages/netlify-cms-ui-default/package.json

@@ -8,14 +8,17 @@
     "netlify-cms"
   ],
   "scripts": {
-    "build": "parcel build src --out-dir ."
+    "watch": "parcel watch src/*.js --out-dir . --no-cache",
+    "build": "parcel build src/*.js --out-dir . --no-cache"
   },
   "dependencies": {
     "classnames": "^2.2.5",
+    "emotion": "^9.1.3",
     "lodash": "^4.13.1",
     "prop-types": "^15.5.10",
-    "react": "^16.0.0",
+    "react": "15.x || 16.x",
     "react-aria-menubutton": "^5.1.0",
+    "react-emotion": "^9.2.6",
     "react-toggled": "^1.1.2",
     "react-transition-group": "^2.2.1"
   },