Enable the Debug level when enabling "all debug"

Summary:
The wording on the label suggests that the effect will be a real
full debug, not just the "Info" level.

Test Plan:
When "Enable All Debug" is selected, the level of all categories is set
to "Debug" instead of "Info".

Reviewers: mlaurent

Reviewed By: mlaurent

Subscribers: kde-utils-devel

Differential Revision: https://phabricator.kde.org/D4385