Added form to submit user example scenes

[jf-kelly]

Description

I was working on the idea of adding a new tab for user example projects in the "open project" modal, but I thought it would be better if user examples were also displayed in the "example scenes" tab. I believe it would be too confusing to have two tabs that are both showing example scenes. So, I just added text at the top of this already existing tab that prompts users to submit their scenes, and provides a link to the submission form. As this is different from the original idea, it is still open to discussion of course.

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Related Issue

#346