Better LDAP-Integration

I have made some changes to our observium instance and i think they should go into the normal source code
Changes:

• Display Username and UserLevel on edituser/user_id=... when ldap authentication is enabeld
• Create correct ldap filter with memberof check for userlist
  => Fixes issue when more than 1000 users are in auth_ldap_suffix and result gets cut off
  The new ldap filter includes a memberof statement for Groups in auth_ldap_group so only correct users are in the result