drawable: convert png to xml files

For black or white icons, this commit converts png to xml files (created from
svg pictures). With a xml files, it is not necessary to have a file for each
size or resolution.

Change-Id: I51f5a4499f0c7640369ddc5aa6b88ac019920ffa
Tuleap: #1165
diff --git a/ring-android/app/src/main/res/layout/item_device.xml b/ring-android/app/src/main/res/layout/item_device.xml
index 59e0dc3..9f79f4b 100644
--- a/ring-android/app/src/main/res/layout/item_device.xml
+++ b/ring-android/app/src/main/res/layout/item_device.xml
@@ -27,7 +27,7 @@
         android:layout_height="wrap_content"
         android:layout_alignParentStart="true"
         android:layout_centerVertical="true"
-        app:srcCompat="@drawable/ic_desktop_windows_black_24dp" />
+        app:srcCompat="@drawable/ic_desktop_windows_black" />
 
     <TextView
         android:id="@+id/txt_device_label"