Zero out graph data

[JonFreer]

Currently, if an hour has a count of zero the line chart just connects the last two non-zero values.

[JonFreer]

This has been addressed by returning zero values from the API. This is intensive as it sends surplus data but also now front pads the data with zeros. Maybe it is best to do it client side.

[JonFreer]

Using bucket_gap_fill, but have to set a start point. As the start point needs to be calculated with a sperate request it is not the most efficient.