Improvements

Some performance improvements:

- Use stat instead of ls. This allow improve listing of directories with
symlinks. Symlinks are resolved by File.getCanonicalFile.
- Simplify ls, fileinfo, find and readlink command
- Simplify the parsing of FolderUsage (only type, size and category is
required), and avoid to load a lot of on unused objects
- Add new file datetime information from stat: access, change and modify
- Improve list, find and resolvelink java commands

Signed-off-by: jruesga <jorge@ruesga.com>