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

instead of response

if taxonomy does not exist

If item does not exist

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.

Delete all terms on an item for the given taxonomy

within a taxonomy

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'.

I've just made the factory use an existing record if already created

It appears that JSONField defaults to empty string

So user is redirected to the correct page after uploading data

Make TabbedPage.name and TabInstance.name SlugFields as they are used in URLs. Also rename TabInstance.view_name to tab_type, which is clearer and paralles the dashboard implementation.