Feature/464 contact field

This pull requests solved #464 and #468 : An employer is now able to fill in his contact data in extra contact fields. By that the employer can be reached directly via email/phone or even mail. 
Furthermore there are now contact fields for each job offer which are pre-filled with the contact data of the employer.
Good choice with the reject method but you could use `x.blank?` instead of `x == '' || x == nil` improving it another little bit ;) And the indentation is still missing for both methods.