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

Such dialog allows:
  * show status of operation;
  * control operation using dialog buttons (Abort, Suspend, Resume, etc).

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>
(simple_status_msg_t): simple status message with label and 'Abort' button.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
(FileProgressStatus): change values to avoid overlapping with B_* values.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
Apply status message for directory size calculation.

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>
(edit_buffer_calc_percent): new editor buffer API.

Modify way to calculate persentage: use byte offers instead of line one.

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

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