Change the Launch Screen to use System Background Color (#5608)

* Change the Launch Screen to use System Background Color as the background color, so that people in dark mode aren't blinded when they open the app (forces a darker background instead of white)

* Clean up LaunchScreen.xib to only change the systemBackgroundColor item

Client/Application/LaunchScreen.xib

@@ -18,7 +18,7 @@
                     </constraints>
                 </imageView>
             </subviews>
-            <color key="backgroundColor" white="1" alpha="1" colorSpace="custom" customColorSpace="calibratedWhite"/>
+            <color key="backgroundColor" systemColor="systemBackgroundColor" cocoaTouchSystemColor="whiteColor"/>
             <constraints>
                 <constraint firstItem="8jg-1f-0sB" firstAttribute="centerY" secondItem="iN0-l3-epB" secondAttribute="centerY" id="ITK-hU-DwR"/>
                 <constraint firstItem="8jg-1f-0sB" firstAttribute="centerX" secondItem="iN0-l3-epB" secondAttribute="centerX" id="grm-jt-xY2"/>