Cleanup debugging (categories)
- port to categorized logging using the macros provided by ECM, and export a category file for kdebugsettings;
- bump the version of ECM, and then the version of Frameworks, to the minimum version where the macros are included;
- remove KDE_NO_DEBUG_OUTPUT, previously used by kDebug and superseded like kDebug by Qt categorized logging;
- cleanup of the level of (very) few log messages; in general, all the existing log calls should be rechecked, and either removed or cleaned;
- reword two poorly worded messages.