Implement sign-off workflow

[norbertlaposa]

Use should be able to add comments and approval to each session and hand it over for further approval to another user.

Example sign-off process:

• Martin creates session and makes one or more runs until he is satisfied with the latest result.
• Martin makes a comment on latest result explaining why one item is failing and why it's ok.
• Martin asks Norbert to review with a handover comment.
• Norbert receives email asking to review.
• Norbert checks the reports and add his approval.
• Norbert asks Sam to review.
• Sam checks the reports and add his approval.
• Sam export executive overview showing test run status and approval history.