Add utility methods to Preferences to check if properties are not empty

src/preferences.js

@@ -15,7 +15,6 @@ class Preferences {
     this._userAccessToken = value
   }
 
-
   get trackerSubmitUrl() {
     return this._trackerSubmitUrl
   }
@@ -28,6 +27,18 @@ class Preferences {
     return browser.storage.sync
   }
 
+  hasUserAccessToken() {
+    return null !== this._userAccessToken && 0 < this._userAccessToken.length
+  }
+
+  hasTrackerSubmitUrl() {
+    return null !== this._trackerSubmitUrl && 0 < this._trackerSubmitUrl.length
+  }
+
+  isConfigured() {
+    return this.hasUserAccessToken() && this.hasTrackerSubmitUrl()
+  }
+
   load() {
     const storageGetter = this._storage.get(null)