Changed cost of power armour crafting bench research from free to 2 AI Cores and also requires tech bench 4

- Changed coverage of the undersuit to include both legs as I apparently overlooked this

I wanted the armour to cost more to make to justify the stats however, that doesn't seem to be possible unless I want it costing morre fabrics so I've reduced the blunt resistance quite a bit

- Roughly reduced blunt resistance from 80% to 60% at mastercraft level.