Eliminate "viewsize".

Remove viewsize, because, uh, honestly, it's a feature that never really made much sense to me. I guess to have a smaller rendering surface on ancient-even-for-the-day hardware?

After this change, viewsize is always treated as if it were 100%.
Add vid_hudscale.

vid_hudscale scales the HUD, menus, and console by a given multiplier (for example, 2.0 will double the size of everything). Useful for high-resolution displays.

Note that those images do not get resampled with gl_texscale, so while fractional values will work, they are likely to look terrible.