SEC-2405: Use DirContextAdapter directly from search. Configure OBJECT_FACTORIES on DirContext created for ActiveDirectory.
SEC-2405: Added tests for OBJECT_FACTORIES
SEC-1932 Added PBKDF2PasswordEncoder.

 - Also moved some logic into a new class, AbstractPasswordEncoder. Both PBKDF2PasswordEncoder and the now-simplified StandardPasswordEncoder extend AbstractPasswordEncoder.
 - Added tests for PBKDF2PasswordEncoder .