Scripts/Commands: Some adjustments to make shutdown commands more user-friendly.

- New error message if a shutdown is delayed due to force threshold.
- New status message indicating that a server shutdown was successfully cancelled.

(cherry picked from commit d760219062)

sql/updates/world/master/2017_02_11_24_world_2016_08_06_00_world.sql

@@ -0,0 +1,5 @@
+-- insert new delay notice messages for server shutdown commands
+DELETE FROM `trinity_string` WHERE `entry` IN (11017,11018);
+INSERT INTO `trinity_string` (`entry`,`content_default`) VALUES
+(11017,"Server shutdown delayed to %d seconds as other users are still connected. Specify 'force' to override."),
+(11018,"Server shutdown scheduled for T+%d seconds was successfully cancelled.");