Allow overriding of default role names via setting

[Bochenski]

For cases where you are plugging into a legacy database that already has a role structure, allow the name of admin, restricted, sysadmin etc to be overriden by a setting. The setting name takes the form [Expected Gintellect Role Name]RoleName.

For example to override which role represents the Admin role, you would set the AdminRoleName setting.