Add nicer interface for managing dataset data

[mjumbewu]

Some things it should allow:

• filter by type of place
• hide/show places and submissions from the map
• download in bulk, CSV or GeoJSON, with the ability to select/reorder/rename fields

On second thought, most of this can be done passably by the existing admin interface. It's not the nicest way, but it is 85% there. The main things that it cannot do are:

• Easily export bulk data
• Choose fields to export with bulk data
• Filter/sort places by JSON-blob attributes (like place type)

[BenSturmfels]

We've built something custom along these lines - a log-in based dashboard for project stakeholders that allows them to browse, search and update places, comments and attachments to their particular projects, export as Shapefile and such. Also includes some ability for stakeholders to be able to dynamically update contents of the welcome and FAQ pages shown on front-end. It's not yet in a form that's general-purpose enough to merge into Shareabouts, but I'd be happy to discuss the approach we've taken.