Fixing issues and updating equip method for Watertank Backpack / Defib

### Fixing issues and updating equip method for Watertank Backpack / Defib

>1. Fixes various issues with Backpack Watertanks / Defibs by slapping NODROP on their respective pseudoitems because tracking the ten billion ways that items can go into other items and cause this crap to break is solved by it.
>2. Changes all watertanks and the defib to use the Atmos watertank equip method (Equip on back, then click on with open hand or action button to get nozzle/defib; Click backslot item with nozzle/defib or UI action button to put object away)
>3. Fixes a runtime that could happen if someone melted the Atmos watertank off of you (Or if someone exploded it or something I dont know)
>4. Fixes an unreported issue where if you Drag 'n Dropped the atmos watertank backpack into an occupied hand slot it fell to the floor and then it didn't have to be on your back slot and blah blah I'm an idiot

Fixes #6204 
Fixes #5559 
>implying it's possible to not duplicate the l_ and r_hand thing.
Op 11-dec.-2014 15:19 schreef "Cheridan" <notifications@github.com>:

> In code/game/objects/items/weapons/tanks/watertank.dm
> <https://github.com/tgstation/-tg-station/pull/6223#discussion-diff-21678127>
> :
>
> > +	if(ishuman(src.loc))
> > +		var/mob/living/carbon/human/H = src.loc
> > +		switch(over_object.name)
> > +			if("r_hand")
> > +				if(H.r_hand)
> > +					return
> > +				if(!H.unEquip(src))
> > +					return
> > +				H.put_in_r_hand(src)
> > +			if("l_hand")
> > +				if(H.l_hand)
> > +					return
> > +				if(!H.unEquip(src))
> > +					return
> > +				H.put_in_l_hand(src)
> > +	return
>
> Duplicated cooooode [image: :cry:] [image: :crying_cat_face:] [image:
> :sob:]
>
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> <https://github.com/tgstation/-tg-station/pull/6223/files#r21678127>.
>