Fixed crashes on Android <5

Due to this bug:
https://code.google.com/p/android/issues/detail?id=26251

Author: David Vávra

library/src/main/res/drawable-v21/sdl_button_pressed.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="utf-8"?>
+<shape xmlns:android="http://schemas.android.com/apk/res/android"
+    android:shape="rectangle">
+    <corners android:radius="2dp" />
+    <solid android:color="?sdlPressedColor" />
+</shape>

library/src/main/res/drawable-v21/sdl_list_pressed.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<shape xmlns:android="http://schemas.android.com/apk/res/android"
+    android:shape="rectangle">
+    <solid android:color="?sdlPressedColor" />
+</shape>

library/src/main/res/drawable/sdl_button_pressed.xml

@@ -2,5 +2,5 @@
 <shape xmlns:android="http://schemas.android.com/apk/res/android"
     android:shape="rectangle">
     <corners android:radius="2dp" />
-    <solid android:color="?sdlPressedColor" />
+    <solid android:color="@color/sdl_pressed_light" />
 </shape>

library/src/main/res/drawable/sdl_list_pressed.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
 <shape xmlns:android="http://schemas.android.com/apk/res/android"
     android:shape="rectangle">
-    <solid android:color="?sdlPressedColor" />
+    <solid android:color="@color/sdl_pressed_light" />
 </shape>