Remove pending content from moderators dashboard, move to /pending

[ebarry]

Please describe the desired behavior.

This feature request is part of improving the moderators experience on the site, in preparation for giving classroom teachers moderation privileges.

This feature request is to stop showing spam on /dashboard to moderator and/or admin accounts on publiclab.org. Instead, provide a link in the dashboard sidebar to a new page where pending content may be approved or spammed. Here are the details, worked out with @jywarren and @bronwen9 :

• filter moderation-pending posts from the dashboard
• create /pending page (visible only to moderators/admins)
• /pending should look/work the same as the regular dashboard (full post 'cards' with images).
• Add a notice in the sidebar of moderator's dashboards showing the # of items in "pending" queue linked to /pending (new page)

Additional context (optional)
Feel free to include any applicable: code, screenshots, or gifs.

Once more pending content comes in, i'll add a screenshot!