jscam: Convert cam1-3.{vlo,slo} into cam1-3.js.

In the process:
- Add a new libcampaign.js function, camCallOnce()
- Add a new libcampaign.js order, CAM_ORDER_FOLLOW
- Implement repairing droids managed by libcampaign.js
- Make use of the new functions on earlier levels as well

refs ticket:4234