Revise Stealth

(MISC)

- Moved to generic.  This is partly because Rogue is getting another class category unlocked base and has too many.

- Aggro behavior no longer changes with difficulty.  We don't need hidden behavior like this and the number is pretty small anyway

(STEALTH)

- Enemies no longer share target_last_seen information at all if the target is stealthed.

- Enemies will still chain aggro against stealth to prevent cheese but aquiring you as a target will be delayed by 3 turns.

Shadow Dance:

- No longer clears targets or forces you out of stealth.