Add per-profile option 'BellMode' for choosing the type of bell

There are no GUI elements for controlling that option, so it is a hidden
option at the moment.

To configure this option manually, put following lines into some konsole
profile under ~/.kde4/share/apps/konsole/ :

[Terminal Features]
BellMode=N

Where N could be 0 for system beep, 1 for system notification and 2 for
visual bell. That mapping might change before next major release.




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