Restore startpos_ply_counter() instead of full_moves()

Restore startpos_ply_counter() instead of full_moves()

And pass correct currentPly to TimeManager::init().

This restores old behaviour, in particular now black has
a different timing than white becuase is no more:

currentPly = 2 * fullMoveNumber;

but becomes

2 * (fullMoves - 1) + int(sideToMove == BLACK)

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>