Make life and mana flasks more interesting - allow Rare up to 4-mod

Flasks capped at Magic is a vestige of P1, where 5 rare flasks was deemed too complicated to keep track of all the mods.

In P2 charms are all automatic, leaving you with 2 classic simple button presses.

Allow flasks to be rare in P2 and balance them accordingly.

2 rare flasks in P2 is still less mod density/complexity than 5 magic flasks in P1.