Add a pair of AA batteries, low voltage indicator lamps

[jrddunbr]

For classroom examples, pairs of AA batteries and incandescent indicator lamps are commonly used when displaying series versus parallel circuits.

We should include a new battery model that is 3.0 volts and is literally two massive AA batteries in a holder. Maybe 1, 2, 4, and 6 cell variants would make sense.

Include a new lamp type that is a 3.0V incandescent that is still visible but dimmer at ~1 volt.

[jrddunbr]

Probing around, the "portable battery" and "portable battery pack" were probably based around some standard battery size. So if we can use those items in a battery holder model that would probably work well. Placing the 4 pack would result in a stack of the remaining batteries if inserted into a 1 or 2 slot, while only filling the number of slots remaining in a 6 slot battery model.