The DAGs main page has All/Active/Paused.

It would be nice if we can have also Running Now which will show all the DAGs that have at least 1 in Running of DAG runs:
![Screen Shot 2021-08-25 at 11 30 55](https://user-images.githubusercontent.com/62940116/130756490-647dc664-7528-4eb7-b4d8-515577f7e6bb.png)


For the above example the new DAGs tab of Running Now should show only 2 rows.
The use case is to see easily what DAGs are currently in progress.

"""
    Some endpoints are called by javascript,
    returning json will allow us to more elegantly handle side-effects in-page.
    """
    if request.headers.get("Accept") == "application/json":
        if status == "error" and status_code == 200:
            status_code = 500
        return Response(response=msg, status=status_code, mimetype="application/json")
    else:
        if status:
            flash(msg, status)
        else:
            flash(msg)
        return redirect(origin)
def not_found(error):
    """Show Not Found on screen for any error in the Webserver."""
    return (
        render_template(
            "airflow/error.html",
            hostname=get_hostname() if conf.getboolean("webserver", "EXPOSE_HOSTNAME") else "redact",
            status_code=404,
            error_message="Page cannot be found.",
        ),
        404,
    )
def method_not_allowed(error):