Fix/student matching

Hey guys,

a friend of mine mentioned some time ago that the student match function does not work properly.
As you can <a href="https://www.hpi.uni-potsdam.de/connect/jobportal/de/students?utf8=%E2%9C%93&q=&semester=&academic_program_id=&graduation_id=&programming_language_ids[]=1&programming_language_ids[]=2&programming_language_ids[]=3&programming_language_ids[]=4&programming_language_ids[]=5&programming_language_ids[]=6&programming_language_ids[]=7&programming_language_ids[]=8&programming_language_ids[]=9&programming_language_ids[]=10&programming_language_ids[]=11&programming_language_ids[]=12&programming_language_ids[]=13&programming_language_ids[]=14&programming_language_ids[]=15&programming_language_ids[]=16&programming_language_ids[]=17&programming_language_ids[]=18&commit=Los!">see</a> students are returned who know at least one of the requested programming language but not each one: 
I think I fixed it by this merge request.
I would be glad if you could have a look at it :)