Move IPA specific code from LDAPClient to the ldap2 plugin.

https://fedorahosted.org/freeipa/ticket/3971
Add wrapper for result3 to IPASimpleLDAPObject.

https://fedorahosted.org/freeipa/ticket/3971
Support searches with paged results control in LDAPClient.

https://fedorahosted.org/freeipa/ticket/3971
Refactor indirect membership processing.

A single LDAP search is now used instead of one search per member.

https://fedorahosted.org/freeipa/ticket/3971
Remove unused method get_api of the ldap2 plugin.

https://fedorahosted.org/freeipa/ticket/3971