Map out possible paths for a URL through the app, including rejection and review, and enhance the UI to make routing more transparent

[kmcculloch]

The UI of a URL page really only implements a "happy path" to take an item from seeding through to bagging and description. It's possible to route items back to an earlier stage by unchecking the stage completion box, and it's possible to send an item to "Crawlable" by checking "Do Not Harvest," but these non-standard routings are not intuitive.

I could imagine a UI that's structured around choices at a given step. So a researcher might be asked to open a page, review the information provided by the seeder, and then choose one of three options:

1. This item is crawlable, skip harvesting [which would populate the do not harvest? boolean]
2. This item needs to be harvested [which would unlock the fields to put in harvest recommendations --> then the user would see a "Submit for Harvesting" button, which would populate the researched? boolean]
3. I'm not sure/This item needs review [which would unlock a comment field and put the item into the "Needs Review" state requested in https://github.com/Have a button to flag "problem URLs" #33]

I'm not proposing any data model changes: we already have the boolean fields needed to represent different paths (or those fields would come along with features that are proposed in separate tickets, like 33 above). I'm proposing streamlining the UI so that users can understand where a ticket has been and where it's going without having to check boxes.