[Button] Add uses-sdk to manifest

Author: pjcollins

Button/Properties/AndroidManifest.xml

@@ -1,3 +1,4 @@
 <?xml version="1.0" encoding="utf-8"?>
 <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="mono.samples.button">
+	<uses-sdk android:minSdkVersion="19" android:targetSdkVersion="19" />
 </manifest>