Add cache to the portion of the REST API client that is used by the Spring Security integration

Make sure the Spring Security integration performance does not suffer from the switch from SOAP to REST. There are some cache classes (com.atlassian.crowd.service.cache.CachingUserManager, CachingGroupMembershipManager and CachingGroupManager) that are coupled to the SOAP API and may need to be adapted or replaced when the implementation moves to REST.