Formerly, each widget saved its history self in WIDGET_DESTROY stage.
Thus, history file was read and written as many times as many widgets
with history are in dialog.
Now all widget histories are written to ${XDG_CACHE_HOME}/mc/history
file at one time before dialog destruction.
An ev_history_load_save_t event type is created to use new event engine
to save histories.
Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
cff5925598