Replaced static query var 'company' with dynamic $this->slug

The problem with changing the slug is that the query var remains the same. Let's say I change it to 'organization' then my links become http://mydomain.de/organization/Orga+Name and all the static `get_query_var( 'company' )` functions return empty. Thus the correct template is not loaded.

I think a clever rewrite rule should be able to bend all requests from the custom slug to a static query var. My knowledge of the Rewrite API is too limited so instead I replaced the static 'company' query var with the slug to resolve the issue.