Add page size parameter to LDAP connection

[coudot]

For Active Directory we need to use the page size settings, else we will not be able to list all entries.

[davidcoutadeur]

Should be ok with PR: #42

For now, I think searching multiple entries:

• is not done at all in self-service-password
• is done only in Ltb\Ldap\search function, which I have configured to use paged search

We should keep this is mind while adding more search functions in ltb-common or ssp/service-desk.

TODO:

• add the corresponding test for paged search