Return of the shelter SPY

I think the Shelter SPY should be re-introduced.

Back before 2.2, most spys would spec to use shelter, made possible by popping a nightspider.

Then came 2.2 and the re-balance flop, and now we're stuck with nanites for healing/resists, and I thnik it's fair to say that most players dislike this.
This also makes the 20 PSI levels of the spy almost irrelevant, a shame really, especially when considering how only missions gives PSI xp to spies.

In short, please get us rid of nanites.

Spies can use deflector and protector now.
They could use absorber with a drug and an imp if PPU reqs were brought down a bit (as I suggest elsewhere).
They don't bother because most people feel the slight resist uptick isn't worth the hassle.