check presence of attributes in job_offers, #6
check if start date is before end date in job offers #6
added checkboxes for programming languages #6

issue: only saves one language
fixed issue of last commit #6
added programming languages to show, #5 made checkbox tag clickable #6
Merge branch 'develop-ja' of https://github.com/tkowark/hpi-hiwi-portal into crud-job-offers

Conflicts:
	app/models/job_offer.rb