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.

"""A list of columns to show in the Add form.
        This dynamically calculates additional fields from providers and add
        them to the backing list. This calculation is done exactly once (by
        checking we're referencing the class-level variable instead of the
        instance-level), and only after we enter the request context (to skip
        superfuluous checks done by Flask-Appbuilder on startup).
        """
        if self._add_columns is type(self)._add_columns and has_request_context():
            self._add_columns = [*self._add_columns, *(k for k, _ in self._iter_extra_field_names())]
        return self._add_columns
    @property
    def edit_columns(self) -> list[str]:
        """A list of columns to show in the Edit form.
        This dynamically calculates additional fields from providers and add
        them to the backing list. This calculation is done exactly once (by
        checking we're referencing the class-level variable instead of the
        instance-level), and only after we enter the request context (to skip
        superfuluous checks done by Flask-Appbuilder on startup).
        """
        if self._edit_columns is type(self)._edit_columns and has_request_context():
            self._edit_columns = [*self._edit_columns, *(k for k, _ in self._iter_extra_field_names())]
        return self._edit_columns
    @action("muldelete", "Delete", "Are you sure you want to delete selected records?", single=False)
    @auth.has_access(
        [
            (permissions.ACTION_CAN_EDIT, permissions.RESOURCE_DAG),
        ]
    )
    def action_muldelete(self, items):