Added point light glow fade for lights that are too close to the camera

[nicholas477]

Adds a point light glow fade for lights that are too close to the camera. This is to make torches/lamps/etc that the player is carrying not blow out the entire screen with their glow.

The PR adds 3 settings: point_glow_min_fade_dist, point_glow_max_fade_dist, point_glow_fade.

• point_glow_min_fade_dist: the distance from the camera that lights start to fade in. The strength of lights closer than this distance is multiplied by point_glow_fade.
• point_glow_max_fade_dist: any light farther than this does not have its glow altered
• point_glow_fade: the maximum amount that point lights will be faded out. So if this is set at 0.2, lights closer than point_glow_min_fade_dist will be multiplied by 0.2

Comparison shots:

point_glow_fade on with default settings

no point_glow_fade

[zesterer]

Funnily enough, this looks a lot like this MR for Veloren