LDAP Wizard: get correct total no of users, groups and complete list of groups on big setups

How to test: 

- have an OpenLDAP with a soft sizeLimit of 500 and a hard sizeLimit of 2000. (works for AD, too, only it does not have a hard limit by default). 
- have 1700 of both users and groups
- use the wizard to configure the LDAP server
- on the User Filter tab the amount of found users is shown in the lower left
 - before: 500
 - now: 1700
- on the Group Filter tab select the proper object class. The amount of found users is shown in the lower left
 - before: 500
 - now: 1700
- on the Group Filter Tab the Group multiselect box shows
 - before:  500 groups
 - now all: 1700 groups

It also fixes what is resolved in #8975 and thus replaces that PR.

Please test/review @PVince81 @ser72 @bboule @Xenopathic  @icewind1991 or others