Add 'Page' level applet/dashboards

[bctcvai]

On the media listing page, it would be helpful to add Page-level applets or dashboards. These would supplement the navigation experience near 'All Media' in the project-detail view.

A registered page-level dashboard could contain:

• Static text / rendered markdown / documentation
• Forms, interactive elements
• Tools to enable summaries, etc.

In the list below, each 'Page' applet could be listed below "All Media", likely with a default and override-able icon. If possible it'd be nice to override the default landing for a given project if it had a Page applet that was better suited to land at then All Media.

[bctcvai]

Completed in 1.4