[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.
- [x] No power load. Briefly works after round start/breaker/power channel toggling before going to 0. No clue as to why, functions in /tg/'s code base.
- [ ] Power channel toggling on/off when? Currently when APC battery charge is at 0/15/30% of a standard size battery max charge.
- [ ] Restore per APC power balancing.

**Testing**
- [x] Check if Z-level support remains as functional as before.
- [ ] Conduct further local testing.
Without knowing anything I would look at where they call ```auto_use_power()``` if I wanted to figure out what they're doing differently.  For us, it's in the master controller and only when the area's powerupdate  is non-zero, which is why lastused_* gets zeroed out.

As for the load-balancing I was planning to look into that as well, probably by Wednesday or so. Otherwise, if you want to take a crack at it, the relevant is in powernet/reset() and apc/process() on our master branch. It might help to compare them between v0.1.14 and v0.1.15.