Sort imports from all files

Add "prettier" script in `package.json` to check if all files are
compliant.

Sort all imports and format all files by running `npm run lint -- --fix`
followed by `npm run prettier -- --write`.

Gitlab #29

Change-Id: Id80402d1344c3bc611f66a46cffeee5f2c375bd8
diff --git a/package.json b/package.json
index e920abe..b2ce7e1 100644
--- a/package.json
+++ b/package.json
@@ -14,6 +14,7 @@
     "clean-all": "npm run clean && rm -rf node_modules client/node_modules",
     "lint": "eslint \"**/*.{ts,tsx,js,jsx}\"",
     "prepare": "husky install",
+    "prettier": "prettier -c \"**/*.{ts,tsx,js,jsx,json}\"",
     "start": "nodemon",
     "start:prod": "NODE_ENV=production node dist/app.js"
   },