Implemented a custom TableCellRenderer to render the table headers
Added code to detect clicks on table headers
Added class com.github.fritaly.dualcommander.SimpleFileComparator to support a simpler file sort "a la OSX"
Simplified code
Added a new table column (at index 0) to represent the type (file / folder) of a file entry
Added enum com.github.fritaly.dualcommander.SortCriteria to easily configure the criteria when sorting files
Added class com.github.fritaly.dualcommander.ConfigurableFileComparator to configure the comparison of files
Clicking on column headers now sort the entries accordingly
Added utility method com.github.fritaly.dualcommander.Utils.negate(Comparator<T>) to easily invert the logic of a comparator
The file entries can now be sorted in ascending / descending order by clicking on the column headers