Use Hor+ for FOV calculations to prevent the default FOV from being too low

[Calinou]

Related to #1382.

Right now, the field of view is defined as an horizontal value, which means wider aspect ratios won't use a wider FOV. This leads to a FOV that's too low on 16:9 displays, or worse, 21:9 displays.

We can fix this by either:

• Using vertical FOV values. This is what games like Minecraft do, but it loses the familiarity with nearly all Quake-based games out there.
• Using horizontal FOV values, but scaling them to match the aspect ratio compared to to the base 4:3.

Implementing this will improve the out of the box experience for players who are using widescreen, which is very common by now.

See this Wikipedia page for more information.