Stop IDE from resetting Video Mode

Just a minor tweak and my first pull ever. :)

With the IDE App class the video mode is set twice. The first time in the PolyCore derived class constructor and the second time at the bottom of the IDE App constructor. The first time this is done the width is set to 900, the second it is set to 1100.

This causes issues with SDL on Ubuntu 12.10. When the video mode is set twice with differing resolutions there appears to be a constant stream of resize events. With every odd sequence having a width of 900 and every even sequence having a width of 1100. This results in the screen constantly flicking between two resolutions.

My impression is that removing this line shouldn't cause an issue on other operating systems as the other derived PolyCore classes all set the video mode in the constructor.