Async UCI options actions

Async UCI options actions

Introduce 'on change' actions that are triggered as soon as
an UCI option is changed by the GUI. This allows to set hash
size before to start the game, helpful especially on very fast
TC and big TT size.

As a side effect remove the 'button' type option, that now
is managed as a 'check' type.

No functional change.

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