Change "1-Monitor" Button to "Fullscreen" Button

[wagneral]

One point on the users wishlist during our workshops was to change the named "1-monitor" button in the control interface to a kind of "fullsize" or "maximize" icon. When only one file is uploaded, the user does not necessarily know that he can show a centered and (if big enough) fullsize display of the contribution on the team monitor. Perhaps this can be illustrated with the well know "maximize" icon (for arrows pointing to the direction of the 4 monitor corners).

[dennmuel]

Alternatively, we could just make the layout default to g1x1 so the first uploaded item gets displayed full screen. I guess that's the most common use case, anyway.