Add minimal PWA (#34)

package.json

@@ -1,7 +1,6 @@
 {
   "name": "vikunja-frontend",
   "version": "0.8.0",
-  "license": "LGPL-3.0-or-later",
   "private": true,
   "scripts": {
     "serve": "vue-cli-service serve",
@@ -12,6 +11,7 @@
     "bulma": "^0.7.1",
     "copy-to-clipboard": "^3.2.0",
     "lodash": "^4.17.11",
+    "register-service-worker": "^1.6.2",
     "v-tooltip": "^2.0.0-rc.33",
     "verte": "^0.0.12",
     "vue": "^2.5.17",
@@ -22,8 +22,10 @@
     "@fortawesome/free-regular-svg-icons": "^5",
     "@fortawesome/free-solid-svg-icons": "^5",
     "@fortawesome/vue-fontawesome": "^0.1.1",
+    "@vue/cli": "^4.0.1",
     "@vue/cli-plugin-babel": "^3.0.1",
     "@vue/cli-plugin-eslint": "^3.0.1",
+    "@vue/cli-plugin-pwa": "^4.0.0",
     "@vue/cli-service": "^3.9.2",
     "axios": "^0.19.0",
     "bulmaswatch": "^0.7.1",
@@ -60,5 +62,6 @@
     "> 1%",
     "last 2 versions",
     "not ie <= 8"
-  ]
+  ],
+  "license": "LGPL-3.0-or-later"
 }