PLFM-2128

- Changes UserManagerImpl to use the GroupMembersDAO for group-related tasks.
- Caching (disabled) of other user information is kept in place.
- Affected method of TestUserDAO is moved to a new TestGroupMembersDAO.
UserDAO changes

- Added stub for new UserDAO for next stack.  To be shunted in place of the current UserDAOProxy.
- Chopped off now-unused portions of the CrowdUserDAO and associated methods/tests