[SpringSecurity] 중복 로그인 제거

링크: http://docs.spring.io/spring-security/site/docs/3.2.3.RELEASE/reference/htmlsingle/#concurrent-sessions

오류시 대처사항: http://stackoverflow.com/questions/8586824/spring-security-concurrency-control

링크: http://ilikesura.tistory.com/entry/%EC%A4%91%EB%B3%B5%EB%A1%9C%EA%B7%B8%EC%9D%B8-%EC%84%B8%EC%85%98-%EA%B4%80%EB%A6%AC%ED%95%98%EA%B8%B0-%EC%84%A4%EC%A0%95%EB%B2%95