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

It appears that JSONField defaults to empty string

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.

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

Also added test

Don't use Bootstrap tabs for our tabbed navigation, as those are meant for single page applications, not for links that reload the page.

use view_name instead of name when getting tab out of the registry

Also refactored some of the tests to pick out the args of interest
sent to render_string

Register the template tag. Also use the view name, not the tab name, when fetching the tab to render.

Fix url patterns. We could fix the single regexp, but apparently best practice is to have this on multiple lines.

I'm surprised that JSONField isn't defaulting to {}, as it says
in the documentation. Need to investigate this.

As Dashboard has WidgetInstance objects, TabbedPage has TabInstance