Add getSectorColormap and P_GetSectorLightLevelAt

Test script: getSectorColormap-test.lua

New:

Function	Parameters	Description	Returns
v.getSectorColormap	sector sec, fixed x, fixed y, fixed z, [int lightlevel]	Returns the sector sec's colormap translation at the specified XYZ coordinates. sec can be nil, making the call equivalent to v.getSectorColormap(R_PointInSubsector(x, y).sector, x, y, z). lightlevel is optional, and ranges from 0 to 255. If the sector has no colormap applied, this returns the COLORMAP file.	Translation (colormap_t)
P_GetSectorLightLevelAt	sector sec, fixed x, fixed y, fixed z	Returns the sector sec's light level at the specified XYZ coordinates. sec can be nil, making the call equivalent to P_GetSectorLightLevelAt(R_PointInSubsector(x, y).sector, x, y, z)	number

Removed:

colormap from extracolormap_t.