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.
This should be merged as the name changed on the contact model. And I still think just merge would be a better name ;)