Update installer UI with more user-friendly permissions options

[allen]

From Tony Arnold:

Under settings, the octal permissions are getting out of control (and they're wrong). S3 should not be suggesting 0777 or 0666 without a warning - plenty of hosts will stop serving content from directories that use these permissions, and it's bad security form too. Generally when I'm developing locally I use 0775 for directories and 0664 for files. Suggesting anything in the 06XX range for directories will mean that you risk being unable to list the contents of the directory. Has any thought been given to making this nice and simple? I'm thinking it should be more user friendly.

Octal perms are fine for people who have UNIX exposure, but a lot of Symphony's audience appear to be designers with little (if any) programming or UNIX exposure. There either needs to be warnings & documentation shown, or a refit of the UI here. This seems to be a real sticking point in the community - I've seen a few healthy discussions erupt recommending 0777/0666 in production environments (bad, bad, bad).

[allen]

From Alistair:

He makes a good point. Perhaps we need make it harder to change. Default to 0775/0664, but allow advanced users to change it with a 'change' button or some such. Give them a plain text input to set whatever they want.