[MIRROR] Color standardization, vars moved, and signals (#194)

* Color standardization, vars moved, and signals (#52574)

    Defined all the existing light_color values.
    Moved their definitions to colors.dm
    Made white the default color. It was so already, but that was very obscured.
    Moved the atom light-related variables to the atom definition.
    Wrapped changes to variables such as light_color into procs that report the event through signals.
    Moved the light_on variable to the atom level, also adding a signal for its changing, to represent toggling lights.
    Cleaned up a little bit of code in where new variables were defined before redefinitions.

This is all atomization to reduce changes in #52413
None of this affect gameplay at all, it's all code cleaning and refactoring.

There's more colors to standardize, a search for color = will find lots of targets, and I see little need to have both the LIGHT_COLOR and COLOR patterns, but I don't want to make this PR bigger than it already is.

* Color standardization, vars moved, and signals

Co-authored-by: Rohesie <rohesie@gmail.com>

code/modules/library/soapstone.dm

@@ -151,7 +151,7 @@
 	var/hash = md5(hidden_message)
 	var/newcolor = copytext_char(hash, 1, 7)
 	add_atom_colour("#[newcolor]", FIXED_COLOUR_PRIORITY)
-	light_color = "#[newcolor]"
+	set_light_color("#[newcolor]")
 	set_light(1)
 
 /obj/structure/chisel_message/proc/pack()