Show current theme in theme selector.

src/components/style_switcher/style_switcher.js

@@ -1,8 +1,10 @@
 export default {
-  data: () => ({
+  data () {
+    return {
       availableStyles: [],
-    selected: false
+      selected: this.$store.state.config.theme
-  }),
+    }
+  },
   created () {
     const self = this
     window.fetch('/static/css/themes.json')