Change GlowingLine minimum size to 8

[XenonA7]

The GlowingLine entity would be much easier to place if the minimum x/y size was 8. Right now you can't create a new GlowingLine entity smaller than x=16 or y=16. Here is a vanilla example where the size is using y=8, this is not currently possible in the editor when creating a new GlowingLine.

[Vegita2]

Is this the only entity where that's the case?

[XenonA7]

The only potential other one I can think of is FerroLine but that entity isn't supported by the map editor anyways (this is from the post-game DLC).

[lexisother]

Speaking of... we should really look into supporting extensions.