Ability to "save" a natal chart

[lfborjas]

It'd be nice to link to one's chart using a username, something like freenatalchart.xyz/charts/lfborjas. We'd need to introduce DB backing naturally, but this does allow us to cache/pre-calculate some stuff, maybe work on some insights, as well as just easier to digest URLs. The downsides are of course privacy concerns, though I would like to make this optional and make it explicit that the charts are public; and then there's the whole maintenance of one's "account" page.

For now though, both the natal chart and transit pages are bookmarkable, so one can already "save" it.