created new homepage
added 5 latest job offers and 3 latest employers
deleted sessioncontroller #326
fixed tests
only shows latest jobs and employers if they exist #326
included root link in menu for staff and student #326
fixed layout problem with sidebar #372
Merge remote-tracking branch 'origin/develop' into feature/new-homepage

Conflicts:
	app/views/layouts/application.html.erb
Merge pull request #372 from hpi-swt2/feature/new-homepage

Feature/new homepage