CSV export button

[sbrl]

Now that the HTTP API supports CSV, we should add a button tot he device graph UI to export a CSV of the currently displayed data.

Perhaps we could also add an option for a 'high-quality' export too, where it doesn't average the data over such long time periods.

We'd need to ensure that we stream large datasets appropriately though if we encounter issues.

[Mr-Pepp]

Hey I'm going to work on this.

[sbrl]

Great, @Mr-Pepp! I suggest creating a new branch from the current dev. The easiest way to do this is to edit a file on the dev branch of this repository using the web interface. It will create a new up-to-date branch for you automatically, and it saves you the to be honest really quite complicated process of updating your existing fork.