Presets for per-node configurations

Issue Summary

Hi there,

I'd like to code up a patch for this module but I figure i'd check-in before starting work. I'd like to be able to allow users to select a preset collection of per-node permissions, so that as an admin I can configure bunches of permissions such as 'public', 'community only', 'admin only' etc, and then tell my users to select a preset, instead of detailing for them each configuration they might need.

I think the workflow would look something like this:

1. Admin creates and configures a series of presets in admin->content access.
2. Admin goes to content-types and enables 'per node content-access'. Once it is selected, additional options appear: 'Allow use of these presets' with multi-checkbox list of presets.
3. When the user goes to the content-access tab on a node, they may either select a preset, or do the config manually as before.