Prepare Dark Theme

Remove the [UIApplication statusBarHidden] use (deprecated since iOS 9).
Use the default UIViewController-based status bar system.

Hide the user interface theme option in Settings.

https://github.com/vector-im/riot-meta/issues/22

Riot/ViewController/CallViewController.m

@@ -124,6 +124,12 @@
     self.defaultBarTintColor = kRiotSecondaryBgColor;
 }
 
+- (BOOL)prefersStatusBarHidden
+{
+    // Hide the status bar on the call view controller.
+    return YES;
+}
+
 - (void)viewDidLayoutSubviews
 {
     [super viewDidLayoutSubviews];