add equals and hashCode methods for every DTO about article.
add equals and hashCode method for CodeDTO.
add equals and hashCode methods for every DTO about contest.
add equals and hashCode methods for every DTO about contest problem.
add equals and hashCode methods for ContestUserDTO.
add equals and hashCode methods for DepartmentDTO.
add equals and hashCode methods for LanguageDTO.
add equals and hashCode methods for every DTO about message.
add equals and hashCode methods for every DTO about problem.
add equals and hashCode methods for every DTO about status.
add equals and hashCode methods for every DTO about team.
add equals and hashCode methods for every DTO about team user.
add equals and hashCode methods for every DTO about user.
add equals and hashCode methods for UserSerialKeyDTO.
Merge pull request #124 from pfctgeorge/equals-and-hashCode-methods

equals and hashCode methods for DTOs