add canonical id to feedback questions

[codersquid]

When a user clicks on the feedback link, the canonical id of the machine will be included in the subject line of the question.

This satisfies #124.

[webteam-app]

Demo starting at https://certification-ubuntu-com-125.demos.haus

[codersquid]

Test by going to a machine page in the demo and clicking on the "let us know" link to see that the canonical id is now included in the subject line of the question (please do not actually create the question).

For example, https://certification-ubuntu-com-125.demos.haus/hardware/201612-25299