FindBugs: more correct fix for default enabled detectors & categories.

This commit reverts previous fixes in commits b7515297 & 4dff88f2 and 
make corrections in one line: replace defaut preferences creation from FindBugsPreferenceInitializer  to UserPreferences.

FindBugsPreferenceInitializer performs UserPreferences creation  and 
apply _eclipse_ defaults.
Merge pull request #42 from NEXSTEP/master

FindBugs: more correct fix for default enabled detectors & categories.