Add support for configurable mapping of group names to role names

As an application integrator, I would like to map multiple Crowd group names to my application role names.

With the Spring integration in Crowd 2.5, there are two mechanisms to grant Spring authority roles to users:

1. Transforming each membership into a role, which names are optionally prepended with a prefix (e.g., ROLE_crowd_administrators).
2. Granting a single authority (e.g., ROLE_ADMIN) to every user which membership intersects with the groups that are granted access to the application.

Therefore, it is not possible to have multiple roles AND fully configurable names at the same time. For instance, if my application uses authorities ROLE_ADMIN and ROLE_USER, I need the groups to be named ADMIN and USER in Crowd, because I can only prepend them with a prefix.