GUI Size Adjuster & Impact Marker Modifications

[TonkaCrash]

Changed GUI Size buttons to scale with GUI size changes and to sized so the pair are the same width as the impact marker hide/show button. The goal was to make them less obtrusive on the screen. Also changed to up/down arrows.

I have GUI size on a HUD because my main PC is a 32" 4K monitor, but I frequently remote in from a MacBook, so I rescale my GUI frequently. The old buttons were oversized.

[TonkaCrash]

I wanted submit these as separate PRs, but Github lumped them into one. The second commit redesigned the Impact Marker to cover less of the terrain at the impact point. The outer ring is the same, but the middle ring is 1/3 the thickness and the inner circle is now a ring half the thickness of the new middle ring, but the same outer diameter as the original circle. This is really the mod designer's choice, but I was wanting the marker to cover less terrain at the touchdown point. Having played with this change a couple months, I'm really liking it. The open circle is about the footprint of many of my landers, so this is a good way to see if the landing point is clear of boulders when using Parallax that adds terrain scatter you can collide with.