Simplify the PRNG code and usage

The patch replaces the concept of magic boosters by a set a well chosen PRNG seeds, allowing 30% quicker magics init; a simpler PRNG design particularly easy to seed; and for skill handicap play, does away with RNG sequence skipping.

Passed STC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 17668 W: 3628 L: 3500 D: 10540

and LTC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 73703 W: 12281 L: 12245 D: 49177