SEC-2690: Support static nested groups in LDAP

This refers to groups that have member: <another group DN> as an attribute
- Add in a utility method in the SpringSecurityLdapTemplate to retrieve multiple attributes and their values from an LDAP record
- Make the DefaultLdapAuthoritiesPopulator more extensible
- Add an LdapAuthority object that holds the DN in addition to other group attributes
- Add a NestedLdapAuthoritiesPopulator to search statically nested groups
SEC-2690: Formatting cleanup
SEC-2690: Revert explicit TcpTransport since causes tests to fail
SEC-2690: String[]->List<String>

Use Collections rather than Arrays since Collections can be immutable.
SEC-2690: Polish method modifiers

- Make methods final where possible
- Make methods private where possible
SEC-2690: Polish LdapAuthority

- Make dn required (as javadoc inidicates)
- Simplify .equals since role cannot be null
- Formatting polish
SEC-2690: Add guard around debug statement