Improve handling of timezones

[sxppro]

Using https://github.com/date-fns/tz

[sxppro]

There are still a few components that use new Date(), these may be removed or fixed later

[sxppro]

I think this is mostly done, although will have to do some more checks to ensure everything is cleaned up and converted to use TZDate or if methods have to work with Date, ensure they respect the timezone using { in: tz(TZ) } or some other way

[sxppro]

Aggregation pipelines that utilise $densify, e.g. monthly spending over time, are all hardcoded to group using UTC time, so they will consider UTC months only. $densify struggles with daylight-saving, adding in additional items to the result, see: https://www.mongodb.com/community/forums/t/bug-densify-and-daylight-saving/206378/2