Add methods to better handle user roles inside a space

We need to add some methods to better handle user roles. Here are 2 examples:

/**

• @return the list of roles the specified user has in the specified space
  */
  List getRoles(String spaceName, String memberName);

/**

• @ return the list of members of the specified space that have the given role
  */
  List getMembers(String spaceName, String roleName);