Renamed FilesSingleton to Synchronizer as it does delegates the different parts of the synchronizing to the right classes.
Added a JsonWatcher to watch the directory where the json files are saved for changes.
Changed JsonDownloader to only copy temp files to the real files if they differ for them current real files.
Added Apache Commons library to use the FileUtils class for checking same content.
Changed JsonDownloader to use FileUtils for downloading files from URLs.
Refactored Synchronizer to define different paths in methods.
 - These methods can be used by all other classes as well, so no paths need to be passed around.
 - To change a path only one method need to be changed now.