Create a welcome screen

[tomitrescak]

• [x] - Show a welcome message
• [x] Two Radios - What is your role (Teacher / Student)
• [x] Store selection in Session Storage
• [x] Redirect to given URLs
  • teachers /admin/assignments (what Divik already has + extra functionality #8 )
  • students /assignments #9

[tomitrescak]

• [x] Those radios are not centred.
• [x] Redirect to proper URLs