solid/udisks2: Add support for categorized logging

Summary:
Allow users to enable/disable messages from the UDisks2 backend to aid
debugging issues seen only in specific configurations.

Debug levels of individual messages is unchanged, these likely needs
some further refinement.

Test Plan:
Run:
./bin/solid-hardware5 listen
QT_LOGGING_RULES="org.kde.solid.*.debug=false" ./bin/solid-hardware5 listen
QT_LOGGING_RULES="org.kde.solid.*.debug=true" ./bin/solid-hardware5 listen
Plug/unplug USB storage device

-> first two invocations show same output as before
-> third invocation shows additional output, added/lost interfaces

Reviewers: Frameworks, broulik

Reviewed By: broulik

Subscribers: broulik, kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D15090