Display text permissions instead of octal

[Dave Shoreman]

775 works great and all, but it would be much easier to understand for a lot of people if it was represented as text, eg:

0600 -> rw-------
0664 -> rw-rw-r--
0775 -> rwxrwxr-x

If it doesn't clutter the UI too much, it could be useful to have a toggle switch somewhere so both representations can be supported.