Merge Connected and Candidate

These two notions are very correlated. Since connected has the most
generality, it makes sense to generalize it to encompass what is
covered by candidate.

STC:
LLR: 4.03 (-2.94,2.94) [-3.00,1.00]
Total: 11970 W: 2577 L: 2379 D: 7014

LTC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 13194 W: 2389 L: 2255 D: 8550

bench 7328585

src/main.cpp

@@ -36,7 +36,6 @@ int main(int argc, char* argv[]) {
   Position::init();
   Bitbases::init_kpk();
   Search::init();
-  Pawns::init();
   Eval::init();
   Threads.init();
   TT.resize(Options["Hash"]);