## Is your feature request related to a problem?

A user mentioned needing a feature to clone dashboards as they create the same dashboard multiple times, each for a different end-customer. Given that we are already planning on doing default / custom dashboards (#1659) we can add this functionality to facilitate dashboard creation.

## Describe the solution you'd like

Simple functionality to duplicate a dashboard.
- Add "Duplicate" button to dashboard list and clone dashboard (e.g. "Copy - AARRR").
![screenshot](https://user-images.githubusercontent.com/5864173/93866745-fce46100-fcbf-11ea-8c96-b1acfb1981d5.png)


## Describe alternatives you've considered
Re-create the dashboard manually.


## Additional context
No additional context.


#### *Thank you* for your feature request – we love each and every one!

posthog/api/test/test_dashboard.py
dashboard = Dashboard.objects.create(name="asdasd", pinned=True, team=self.team)
        response = self.client.post(
            "/api/dashboard_item/",
            {"filters": {"hello": "test"}, "dashboard": dashboard.pk, "name": "another"},
            format="json",
        ).json()
        self.client.patch(
            "/api/dashboard_item/layouts/",
            {
                "items": [
                    {
                        "id": response["id"],
                        "layouts": {
                            "lg": {"x": "0", "y": "0", "w": "6", "h": "5"},
                            "sm": {"w": "7", "h": "5", "x": "0", "y": "0", "moved": "False", "static": "False",},
                            "xs": {"x": "0", "y": "0", "w": "6", "h": "5"},
                            "xxs": {"x": "0", "y": "0", "w": "2", "h": "5"},
                        },
                    }
                ]
            },
            format="json",
        )
        items_response = self.client.get("/api/dashboard_item/{}/".format(response["id"])).json()
        self.assertTrue("lg" in items_response["layouts"])
    def test_dashboard_from_template(self):