Move foreman LDAP functionality to ldap_fluff

Most logic comes from here: https://github.com/theforeman/foreman/blob/develop/app/models/auth_sources/auth_source_ldap.rb 

and https://github.com/theforeman/foreman/pull/529 , which this PR is meant to facilitate.
I am not sure what you mean.
```ruby
grouplist.map(&:downcase).collect(&(proc { |g| g.sub(/.*?cn=(.*?),.*/, '\1') } ))
#equals
grouplist.map(&:downcase).collect { |g| g.sub(/.*?cn=(.*?),.*/, '\1') }
```