Consider material density in king safety

Consider material density in king safety

Scale king danger of drop variants by material density
and thereby remove magic correction factors.

euroshogi STC
LLR: 2.97 (-2.94,2.94) [0.00,10.00]
Total: 2735 W: 1417 L: 1276 D: 42
http://www.variantfishtest.org:6543/tests/view/5f3fd4266e23db221d9e902e

euroshogi LTC
LLR: 2.95 (-2.94,2.94) [0.00,10.00]
Total: 1427 W: 760 L: 639 D: 28
http://www.variantfishtest.org:6543/tests/view/5f46e1076e23db221d9e9045

shogi STC
LLR: 2.95 (-2.94,2.94) [0.00,10.00]
Total: 6037 W: 3098 L: 2909 D: 30
http://www.variantfishtest.org:6543/tests/view/5f3fabca6e23db221d9e9013

shogi LTC
LLR: 2.98 (-2.94,2.94) [-10.00,5.00]
Total: 917 W: 487 L: 425 D: 5
http://www.variantfishtest.org:6543/tests/view/5f46b5236e23db221d9e9043

judkins STC
LLR: 2.96 (-2.94,2.94) [0.00,10.00]
Total: 2936 W: 1430 L: 1292 D: 214
http://www.variantfishtest.org:6543/tests/view/5f3fd48d6e23db221d9e9030