Robust squash

Squashed version of #5360

Baton rework:
Batons now operate off of power cells. Power cells can be removed with a screwdriver. Each baton has 10 hits worth of charge with the starting cell. The cost is 1000 units of power for both the cell and cyborg cells, though this is easily tweaked down if it cripples secborgs too much in practice.

Improvised weapons:
-Switchblade (Metal + Plasteel)
-Bats (Wooden and metal, fashionable from stacks)
-Spear (Made from metal rods + cablecuffs + glass shard, dangerous.)
-Stunprod, improvised stun baton, made using a rod, cablecuffs, wirecutters, and a power cell. Less-stealthy alternative to stungloves. (We can remove or nerf them now, perhaps.)

Balance tweaking:
Increased time on the weaken from punches and the knock-down on weapon blows. Mildly decreased push time to shift push away from becoming the be-all end-all of single combat again, especially in unarmed situations.

Embed tweaking:
Made embedding much more likely to proc on melee. It was nigh impossible with anything but an e-sword, an axe, or admin-spawned weapons in the past. There is now a minute chance for many more thrown and swung weapons to proc embedding on a hit, and much more likelihood for them to cause significant damage on removal. This was done to increase the lethality of a melee with sharp or not-so-sharp-but-sufficiently-motivated objects.
Uh, you actually want to be dividing by CELLRATE here. You can check out line 1206 of apc.dm for an example. Line 98 of cell_charger.dm is perhaps a cleaner example where we multiply the charge amount given instead.

Yeah, I suppose it can be confusing. Sooner or later I should probably convert all the power cell charge amounts to Watts * time and get rid of CELLRATE. That way the amount of charge given to a cell will equal the amount of power drawn from the area APC (minus efficiency losses, if you want to do that) and we won't keep running into these problems.

The problem with getting it wrong is that charging the stun baton will give the baton's cell way more charge than is drawn from the area APC's power cell, allowing you to recharge the APC for free by swapping the baton's cell with the one in the APC.