Support zooming in/out on the welcome screen

[DanS2D]

By default, the simulator welcome screen targets the lowest common denominator in regards to screen size. It does this to ensure it displays in its entirety, even on tiny 768p resolutions for example.

However, this leaves people with 4k displays like myself with a really small welcome screen window.

The proposal here is for zooming in/out to work in the welcome screen like it does for device skins.

Depending on your display resolution, these settings will have an upper limit of whatever can fit on the screen. So if you pick the huge setting, which is for example 2560x1440 (not real) and you have a display of 640x480, it will pick a size that will fill as much of the available screen area in that 640x480.

[DanS2D]

will be implemented in the next commit.