Deprecate Role::resources in favor of Role::allocated and Role::offered.

There are upcoming enhancements around role related resource accounting. The changes will add a more detailed role related resources accounting.

We need to retire the resources member of the Role Message in mesos.proto (V0 + V1). This in turn means that we follow this deprecation on the role-related endpoints as well, adding allocated to both "/roles" as well as "GET_ROLES".