feat: add theme picker (#69)

Add theme picker for configuration of angular material default themes.

Fixes #68

package.json

@@ -37,6 +37,7 @@
     "@angular/platform-browser-dynamic": "^6.0.6",
     "@angular/router": "^6.0.6",
     "@angular/service-worker": "^6.0.6",
+    "@ngx-pwa/local-storage": "^6.0.0-rc.0",
     "@ngx-translate/core": "^10.0.2",
     "@swimlane/ngx-charts": "^8.1.0",
     "angular-archwizard": "^3.0.0",