Move Spare Parts icon to mipmap

So that the different icon densities don't get stripped out of the build
by aapt, move it to the mipmap directory.

This will ensure that any program using the getDrawableByDensity API can
read any density/size of the icon needed.

Change-Id: I48c27f7a8b115365c5827ddaa9e8710f3b81358e

apps/SpareParts/AndroidManifest.xml

@@ -21,7 +21,7 @@
     <uses-permission android:name="android.permission.WRITE_SETTINGS" />
     
     <application android:label="@string/app_label"
-            android:icon="@drawable/app_icon">
+            android:icon="@mipmap/app_icon">
 
         <activity android:name="SpareParts">
             <intent-filter>