This PR changes the historical view of billing so that the graphs are called with a bill_hist_id param instead of from and to. This is used to look up the 95th percentile line and draw this on the graph. This means that when viewing the billing graph for previous months, the relevant 95th percentile line will be drawn on instead of the current value.
This may conflict with #3194 - I'll update whichever one of those gets done second if so!
Make billing graphs take times from bill_hist_id and use that for 95th
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Easier to rebase this one I expect so shall hang fire.
Turns out this didn't clash and no rebase is required.