Some useful little modifications to plugin "identiteam"

Hi, I've dowloaded your plugin, but in my specific installation I've had to modify somthings in the code.
I've a Samba4 server which act as an Active Directory server. I usually made requests against its LDAP backend.

Specifically I've made following modifications :

- Added the ability to set authentication credential against LDAP server
- Added LDAP_OPT_REFERRALS option in order to avoid ldap_search -> "Operations error" in certain configurations (Samba4)

Thank you for this very useful plugin.
Gabriele