Metrics now support timezones

Timezones can be tricky. Until now, our Metrics library used a static timezone for all Metrics, meaning that depending on where you were in the world, you might see some strange data for metrics with data points at the start of end of the month. Ie you're expecting to see a number fall into January, but because of timezones, it falls into February on the chart / table that you're looking at. Now, each Metric can have its own timezone set, which will be respected across the entire system, removing one complexity around timezones!