Updated xdisplay to use opencv2 and publisher queue

Issue reported on @davetcoleman's repo https://github.com/davetcoleman/baxter_cpp/issues/20  and fixed by @jon-weisz's https://github.com/jon-weisz/baxter_cpp/commit/49d47a636ed566753adb8aee5bf7ed20208f1e03. Thanks guys! After applying a cv2 patch to the Indigo Baxter and this fix to baxter_examples, the xdisplay.py example now works as intended on an Indigo workstation. @rethink-rlinsalata, can you verify?