have a local db

[thedavidmeister]

cross posting rainlanguage/rain.orderbook#950 as it needs to apply here

webapp obviously has the constraint of being in a browser, but this doesn't mean that we can't put a db in the browser, it just means that the persistence is up to the browser

this doesn't matter that much for us because we are only trying to cache things anyway, so if the user loses their db it just means rebuilding it from the sg fresh, there's no actual data loss