Polish for Onboarding Carousel

Add dark mode assets and colours.
Improve layout for 12" iPad and 4" iPhone.
Move isLockedToPortraitOnPhone to RiotNavigationController.

Riot/Modules/Common/NavigationController/RiotNavigationController.m

@@ -32,6 +32,11 @@
 
 - (UIInterfaceOrientationMask)supportedInterfaceOrientations
 {
+    if (self.isLockedToPortraitOnPhone && UIDevice.currentDevice.userInterfaceIdiom == UIUserInterfaceIdiomPhone)
+    {
+        return UIInterfaceOrientationMaskPortrait;
+    }
+    
     if (self.topViewController)
     {
         return self.topViewController.supportedInterfaceOrientations;
@@ -67,4 +72,14 @@
     [super pushViewController:viewController animated:animated];
 }
 
+
+- (instancetype)initWithIsLockedToPortraitOnPhone:(BOOL)isLockedToPortraitOnPhone
+{
+    self = [super init];
+    if (self) {
+        self.isLockedToPortraitOnPhone = isLockedToPortraitOnPhone;
+    }
+    return self;
+}
+
 @end