Soft launch banner and feedback survey

[tellyworth]

To soft-launch the plugin for user feedback we need two things:

1. A survey link or feedback form on new plugin directory pages.

2. A banner on the old plugin directory inviting users to try the new directory.

[tellyworth]

Ideally we should commit the banner early with a constant to enable it when ready (and disable if needed).

[mapk]

In 4435:

Notification classes: Notification styling added to wp4.css

I've added some notification styling to wp4.css since .org doesn't seem to have any notification styles already.

See #2267

[mapk]

In 4436:

Notification classes: Adjusting font size to match rest of text on page.

See #2267

[mapk]

In 4437:

Plugin Directory Theme: Updating plugin card styles & adding a feedback survey link.

See #2183, #2267

[tellyworth]

In 4438:

Plugin directory: add feedback link in header.

See #2267

[tellyworth]

In 4442:

Plugin directory theme: always expand the "Share your feedback" link.

See #2267

[samuelsidler]

Milestone Plugin Directory v3 - M9 deleted