Ticket #2136: create status dialog to interrupt long-time operations.

This dialog allows:
  * show status of operation;
  * control operation using dialog buttons.

Status dialog is raised after specified delay after operation start.
If operation duration is less than delay, the status dialog is not raised.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
mcviewer: refactoring of percentage display.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
mcviewer: apply status message for search process.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>