Debugger: Move debugger icons from core to debugger

These three images are exclusively used in the Debugger
plugin, thus belong into the Debugger resources.

Change-Id: I327236c66f7424b8bec94630972844175b793fad
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
Reviewed-by: hjk <hjk121@nokiamail.com>