Rework trap generation

Instead of mostly generating mechanical traps & then squashing
them (except in Slime, which had more than ten times as many
traps as the rest of the game since it never generated mechanical
traps to begin with), just generate magical traps. Should make
traps actually appear in the game again outside Zot, which I think
is good for variety & excitement.

Trap numbers, ratios, etc have been adjusted.
Examples:
D:1:
	Old: 0.4 Tele, 0.35 Shaft
	New: 1.3 Tele, 0.7 Shaft
D:15/Lair:5/S:1:
	Old: 0.08 Zot, 0.05 Alarm, 0.39 Tele, 0.34 Shaft
	New: 0.07 Zot, 0.75 Alarm, 1.5 Tele, 0.75 Shaft
Zot:1
	Old: 2.01 Zot, 0.05 Alarm, 0.39 Tele, 0.34 Shaft
	New: 2.33 Zot, 0.42 Alarm, 0.85 Tele, 0.42 Shaft
This is partially as an experiment for compensating for monsters
setting off one-use tele traps before you ever see them.