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.
You can use compact and join here to join all filled attributes into one string in a oneliner :)
`[name, street, zip_city, email, phone].compact.join('\n')`

And please check the indentation as it does not seem to be two spaces for each new block.