tests: Add image class

Add class for managing XGL image objects in the test framework.
diff --git a/tests/xglimage.cpp b/tests/xglimage.cpp
new file mode 100644
index 0000000..be70a8c
--- /dev/null
+++ b/tests/xglimage.cpp
@@ -0,0 +1,5 @@
+#include "xglimage.h"
+
+XglImage::XglImage()
+{
+}