feat(splash): 原生开屏改为品牌启动图

android/app/src/main/res/drawable-v21/launch_background.xml

@@ -1,4 +1,9 @@
 <?xml version="1.0" encoding="utf-8"?>
 <layer-list xmlns:android="http://schemas.android.com/apk/res/android">
-    <item android:drawable="@color/splash_background" />
+    <item>
+        <bitmap android:gravity="fill" android:src="@drawable/background"/>
+    </item>
+    <item>
+        <bitmap android:gravity="center" android:src="@drawable/splash"/>
+    </item>
 </layer-list>