[DNM] - Ports /tg/'s cable and powernet code

Can now cross cables without transferring power between them, and likely also have two 90-degree/diagonal cables cross the same turf without connecting.
May also resolve issues with powernets not updating correctly, in particular when placing diagonal cables.

**Known points**
- [x] Breaker boxes shall be supported again.
- [x] Port /tg/'s solar code.
- [x] Terminals shall reconnect properly if underlying cable is cut and replaced.
- [x] Optional but much desirable: Complete the port of /tg/'s wire system rather than leave it halfdone.
- [ ] No power load. Briefly works after breaker/power channel toggling before going to 0. More than likely requires /tg/'s "static" power additions as well.

**Testing**
- [x] Check if Z-level support remains as functional as before.
- [ ] Conduct further local testing.
Draw power was changed to ```var/surplus = max(avail - newload, 0)``` for a reason. If I'm not mistaken, if you do this you will allow machines to overdraw from the powernet since this does not take into account what other machines have already drawn.