Add www-data to deploy group

[ericclemmons]

Their relationship should be bi-directional (giggity).

Then maybe we can tone back permissions to 644 and 755 for directories & files, respectively.

[EvanK]

I think, for the sake of sanity and simplicity, we should:

1. Ensure deploy user is a member of www-data group
2. Ensure www-data user is a member of deploy group
3. Ensure the web root is 664 for files, and 775 for directories
4. Ensure the web root is owned entirely by www-data (user and group)

My reasoning for the last item in particular is that many of the strangest permissions issues we've seen thus far (installing/upgrading themes & plugins) appear to be the result not of an operation being prohibited by permissions, but by flaky permission checks within the Wordpress core and plugin codebases

[ericclemmons]

That last item is a good point. Using chmod g+s may be worth doing as part of the setup process. Maybe even cap's " group_writeable" flag will handle this....