Support custom OG roles

#4636

Before:
After setting a vsite to use custom roles and permissions instead of the default ones, it is impossible to assign roles to members. No error, just doesn't work.
In addition, all roles lists did not display the custom roles, just the default ones - it was usually hard-coded, and when a DB query was made, it was made on the default OG roles, not the custom ones.

After:
You can now assign og roles to members, even if the roles are custom. Also, lists of roles now display the right roles.