Fixed Battery.cs

Initial implementation of the script couldn't turn the light back on
upon getting new batteries due to using SetActive(), so I changed it to
take a Light(rather than GameObject) and made it modify the intensity
field of that Light instead.
Fixed Battery.cs

Previous commit's name&title should have belonged to this one. Previous
commit should've been: updated Groucho to count as an obstacle and be
tagged as a monster.