Renamed class com.github.fritaly.dualcommander.ProgramPreferences into UserPreferences
The class com.github.fritaly.dualcommander.UserPreferences can now fire PropertyChangeEvents
Updated class com.github.fritaly.dualcommander.DirectoryBrowser to take into the user preference 'show hidden files'
Implemented saving & reloading of user preferences
Added a compile dependency to Log4J 1.2.17
Configured Log4J to log in DEBUG. Listen to preference change events
Defined constant com.github.fritaly.dualcommander.UserPreferences.PROPERTY_SHOW_HIDDEN
When the user preference 'show hidden' changes, refresh the active directory browsers to show / hide the hidden entries
Added assertions to ensure the init kinematics is enforced