[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.
Using percentage values instead of hardcoded charge levels seems nicer, but then it means that higher capacity power cells aren't as good as they should be, as they blackout sooner than they need to.

Really the optimal method should involve estimating the amount of time left before the cell runs out.