graphs don't handle phptimeseries properly

[djh42]

I've noticed various errors in the presentation of phptimeseries data by the graph module. They're described in a forum thread at https://community.openenergymonitor.org/t/graph-peculiarities-with-phptimeseries/9819

It seems clear these are bugs as no one has suggested any other explanation.

[TrystanLea]

Thanks @djh42