Feedback form modal in sidebar

[RW + FW]

This pull is ready to review, but not merge.

The functionality is here and good, we're just ironing out a few small styling details with @andibyday as well.
This file has multiple specs testing various aspects of this feature. While that's good for isolating failures and speccing things out, it adds to test run time due to Selenium going through the same steps (signing in) for every single test.

Consider changing this to test the happy path and make a few assertions in one `scenario` block (the Capybara DSL equivalent to `it`). It all adds up.