Support aggregation queries with embedded predicates

/**
 * @Indexed(index="team")
 */
message Team {
   /**
    * @Basic
    */
   required string name = 1;
   /**
    * @Embedded(includeDepth=2, structure=NESTED)
    */
   optional Player captain = 2;
   /**
    * @Embedded(includeDepth=2, structure=NESTED)
    */
   repeated Player players = 3;
}

message Player {
   /**
    * @Basic
    */
   required string nick = 1;
}

select count(t) from Team t where t.name = 'fax' and t.captain.nick = 'mark' and t.players.nick is null group by t.name