Fix "overlapping" effect of pictures when using external projector

[utstikkar]

When using an external projector (and resolution might be key here, but I don't have them here), the background pictures seem to overlap as the presentation goes, always leaving the one from the previous slide appear on the top and bottom of the screen.

[gnunicorn]

I first suspected this to be related to aspect ration (as we also have blank border if the windows has a different aspect ration than the screen is set up for) but a bit of debugging I see that actually the HTML seems to be set up correctly covering the entire area as it is supposed to be but the rendering/refreshing of the browser hasn't properly done this yet. Just a gentle resizing of the browser window shows that the issue is gone right away. I suspect this to be a browser bug but nothing we can't work-a-round non-the-less. Browser showing this issue is Chrome 27 with the state of tech presentation. Requires further investigation.