Implement CECP 'setup' command

Implement CECP 'setup' command

On reception of an "info string variant NAME startpos FEN" from the engine
UCI2WB will now send "setup (-) 8x8+0_fairy FEN" to the GUI, to make
engine-defined variants also work with UCI engines. Correct operation
required sending of an 'isready' command to the engine after setting
the UCI_Variant option (which evokes the 'info string' response),
and stalling processing of GUI commands until the 'readyok' response,
to prevent early processing of a following 'ping' before the engine
got time to submit the reply. This way the 'info string' response
can be optional. When variant ="chess" the 'info string' is ignored,
as such a setting of UCI_Variant only occurs in response to 'new',
and never to 'variant'.