Make the update button first in the code so that html5 browsers consider it the default button when pressing enter.

Refactor QUESTION_TYPE_TAXONOMY contanst in ViewAndEditTable into an application-wide constant providing the main categorization taxonomy per item type.

Refactor views into multiple files prior to developing edit item features. Also changed the edit/create item urls.

Only display the Remove Question Type menu item on pages where the
question type can be set.

Ideally I'd like None to represent no category but empty string fits
better with what is on the form for the individual dropdowns. So
let's make that consistent.

Message -> Item and Category -> Question Type

If there is no source set on the tab configuration, the upload
button will no longer be displayed.

Added network_provider column to ItemTable, and ensure it's not displayed in the table widget. Also ensure the widget doesn't display the 'select_item' column, previously named 'delete'.

So user is redirected to the correct page after uploading data

When process_items is called without a request, redirect to data-view (don't try to double guess the tab)

Provide the tab instance to get_context_data, and use that to work out the URL to redirect forms to.

Remove outer html from the view and edit page, this is now taken care of by the tabbed page rendering.