[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.
While you want ```longtermpower < 0``` to be a condition for switching to a more conservative power usage mode, you want ```longtermpower >= 0``` to be a condition for switching in the opposite direction. Otherwise APCs may flicker back and forth between usage modes rapidly.

This was something that was being done with the autoflag, if you look below at the removed code.