Allow leaving feedback on projects from the Project Installer UI.

Sibling-issue (or sub-task depending on how one sees it) to the one for allow voting from backdropcms.org: https://github.com/backdrop-ops/backdropcms.org/issues/246

Most of the items that were here were also listed on the meta issue -- changing the scope of this issue to address only a single sub-item.

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It would be great if anyone who was running a backdrop site could leave feedback for their modules directly from their own website.

This is going to be quite a challenge because this person is going to both need to have a confirmed account, and be logged into the Backdrop site in order for the review to be posted.

Maybe we can come up with a way that we can use a single dummy user for all these comments, but also record the URL of the site submitting the review?

Let's brainstorm other (possibly better) ideas on how we could possibly make this happen.

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Once we have a reasonable proposal, let's move this issue to the project module queue.