Fixed missing imports in SDLActivity (thanks @guusw!)

android-project/app/src/main/java/org/libsdl/app/SDLActivity.java

@@ -27,7 +27,9 @@ import android.os.Build;
 import android.os.Bundle;
 import android.os.Handler;
 import android.os.Message;
+import android.text.Editable;
 import android.text.InputType;
+import android.text.Selection;
 import android.util.DisplayMetrics;
 import android.util.Log;
 import android.util.SparseArray;