Replace i18n by a custom implementation (#638)

There are two problems with the current localization strategy:
- We download the translations on-demand, which means that it does a serial roundtrip for nothing.
- withTranslation helper actually renders the app 3 times on startup, instead of once (I haven't tried to debug it)

package.json

@@ -7,13 +7,10 @@
   ],
   "dependencies": {
     "browser-nativefs": "0.2.0",
-    "i18next": "19.1.0",
     "i18next-browser-languagedetector": "4.0.1",
-    "i18next-xhr-backend": "3.2.2",
     "nanoid": "2.1.10",
     "react": "16.12.0",
     "react-dom": "16.12.0",
-    "react-i18next": "11.3.1",
     "react-scripts": "3.3.0",
     "roughjs": "4.0.4"
   },
@@ -24,7 +21,6 @@
     "@types/jest": "25.1.0",
     "@types/nanoid": "2.1.0",
     "@types/react": "16.9.19",
-    "@types/react-color": "3.0.1",
     "@types/react-dom": "16.9.5",
     "enzyme": "3.11.0",
     "enzyme-adapter-react-16": "1.15.2",