kcachegrind (or dependency?): add "suggests: breeze-icon-theme"

[Simon Sobisch]

Installing kcachegrind with `apt install` leads to a working program, 
but on each start you get a warning message

    Icon theme "breeze" not found.
Fixing this message is possible with `apt install breeze-icon-theme`, 
which makes me believe that this should be suggested (either directly or 
via one of its dependencies).

Regards,
Simon