Initial version of a prev/next button for the web viewer

See also:
http://trac.openmicroscopy.org.uk/ome/ticket/11309
http://www.openmicroscopy.org/community/viewtopic.php?f=4&t=7595

This allows you to browse quickly through a dataset in the full screen image viewer by either using the buttons or the arrow keys. It works by pulling this information from Javascript through `window.opener`. This has as advantage that it can respect filters (still needs to be done). On the downside, it has as consequence that browsing to another dataset in the Webclient window will break the functionality.

Additionally, this could be made to also change the image selected in the Webclient window.

Any comments?