Add support for sticky and hot-swappable feature flags.

app/src/main/java/org/thoughtcrime/securesms/ApplicationContext.java

@@ -150,6 +150,7 @@ public class ApplicationContext extends MultiDexApplication implements DefaultLi
   public void onStart(@NonNull LifecycleOwner owner) {
     isAppVisible = true;
     Log.i(TAG, "App is now visible.");
+    FeatureFlags.refresh();
     ApplicationDependencies.getRecipientCache().warmUp();
     executePendingContactSync();
     KeyCachingService.onAppForegrounded(this);