Spring Security: enable CSRF protection

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@see http://docs.spring.io/spring-security/site/docs/3.2.x/reference/htmlsingle/#csrf

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See also: http://spring.io/blog/2013/08/21/spring-security-3-2-0-rc1-highlights-csrf-protection/

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See also: https://jira.spring.io/browse/SEC-2543