Scale the quad in setup mode when shift is pressed

[Foaly]

It would be nice, if shift is pressed while in setup mode, that the quad will scale like you are used to it from other program. This can easily be achived by modifying the x value of one neighbour coordinate and the y value of the other neighbour coordinate.

On windows, this code detects if the shift key is pressed:

if(((GetKeyState( VK_SHIFT ) & 0x80) > 0))
    std::cout << "Shift" << std::endl;

Requires a cross-platform is-shift-key-pressed-function().