Undefended King Ring

There was already a penalty for squares only defended by King (undefended)

This test records a penalty for completely undefended squares in the so called extended king-ring
(so if we exclude squares defended by a Kg8 for example, we only look at h6 g6 and f6)

We also exclude squares occupied by opponent pieces in this computation,
based on the following results

Was yellow at STC
LLR: -2.97 (-2.94,2.94) [0.00,5.00]
Total: 112499 W: 20649 L: 20293 D: 71557

and passed LTC
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 36805 W: 5100 L: 4857 D: 26848

Bench: 8430233

Resolves: #619