I should be able to see information about Roles when I am selecting them

(Bug, Investigate , Priority: High, Test Status: No automated tests yet , Reported By Justin du Coeur, )
UX, Invites
Summary: Currently, in the Sharing page, you have to choose Roles kind of blind. That's inane -- we should be displaying information about the Roles somewhere convenient.
This needs design, but at the least there should be a "?" button next to each one, which gives a popover with the details.
Roles should gain a Details Property, which is a description of the intent of this Role. Both standard and custom Roles should have this, and it should be displayed in this popover.
The popover should probably also concisely list the Permissions granted by this Role, if any.