[front] Feedback

[cvan]

Before:
https://marketplace-dev.allizom.org/feedback
Here's the old JS

After:
This needs to work for both anonymous and authenticated users. There's no RECAPTCHA, so don't be stupid.

• textarea[name=feedback]
• input[name=platform] (e.g., Gaia, Firefox for Android, etc.)
• input[name=chromeless]
• input[name=from_url]