Added method, some tweaks
Added method, some tweaks

- Added `discoverAdldapFromModel()` method to retrieve the Adldap user
from the eloquent model
- Users are now searched for only if `getBindUserToModel()` is true, to
prevent extra queries for users who do not have it enabled

michaelbonds/Adldap2-Lumen,strebl/Adldap2-laravel,Adldap2/Adldap2-laravel,minkbear/Adldap2-Laravel