Cleans up used_radios

The used_radios handling was too specific to be in mob/living/say.
Subtypes had to figure out what to pass for used_radios anyways, they
can also decide how to handle radio use (or if talking into radios even
applies to their mob type).
Allows properly keyed headsets to broadcast in robot talk and/or hivemind

Adds :0 speech code which activates radio-defined behaviour.
Removes unused radio code, world print in forcesay
Ports /tg's cable and powernet code to our code base.
Cherry picking breaker box fix.
Adds diagonal cable check on breaker box state change.
Basically ripped over /tg/'s powernet and cable code into our own codebase.

Keeps Z-level code as it was.
Modifies/restores powernet procs as necessary to match our own implementation changes.
/tg/'s solar code with a fix for the solar control computer not refreshing on user input.
Converts all machines relying on RandomAPCWires() to the new wire datum system.
Fixes bad tabbing, only evident when placing Z-crossing cables.
Sets turn-off limits based on a standard cell's max charge
Master controller no longer annihilate powernets, powernets annihilate themselves.

Some misc. changes.
Fixes #6754.

All station pipes should again be properly layered when floor tiles are installed, etc.
Added a worn icon for rainbow cap, previously only flipped would work.
Makes heist unvotable and fixes the language bug with spawned vox.
Merge pull request #6760 from Zuhayr/master

Removes heist as a votable roundtype.
removing world debug message.
sanity check on facehuggers.
xenos need to hiss too
Merge pull request #6761 from DJSnapshot/hotfix

Xeno fixes and world debug message removal.