Configure units of light sources and convert per scene

[lupestro]

Token light values in Foundry are in the units of the scene in which they are used. By applying our dim and bright light values to these directly, we are currently erroneously assuming that all scenes in a game will be configured to use the default units of the game system rulebooks upon which our light values are based. As a result, we end up with a single character shedding light ten feet in one scene and ten yards in another scene in the same game.

Mitigation:

• In the predefined light sources, for each light source, specify the units of distance that the dim and bright numbers represent.
• Add support for units to the user light sources schema and plumb them through.
• When applying a light to a character token in a scene, convert the units in the light source definition to the units used by the scene before applying them to the token.