allow point lights to be linked to triggers

[Jigoku]

Allows light entities to be directly linked to a trigger.

There are a few use cases for this feature, one being that light sources for a sword weapon spawn (eg;volumetric light above the weapon platform) can be hidden when $mutsbitclassic isn't set.

I'm not sure if i've missed anything, but seems to work fine from my testing locally.

[Jigoku]

~~Found a problem with this PR, existing maps end up with no lights emitting anything (even a /newent light). However, only a newmap being saved/loaded will allow lights to emit. Not sure why that happens though.~~

I think this is resolved. But not sure on the usage of setting e.setspawned(1) where it currently is.

[q009]

I'd squash those commits into one

[qreeves]

I will get to this, but I have to be a bit more thorough with things that mess with entities and triggers.

[Jigoku]

fixed conflicts and using getlightfx() as suggested for the spawned check