Repeated overpass querying when in a location without a POI

[Teester]

A side effect of #16: When in a location without any overpass results and location results have relatively poor accuracy, the location can flick between low and high accuracy, making it look like you're moving around.
So, queries keep being run as there is nothing in the database to say that you've been at that location before. We need to store locations of queries in the database as well as queried POIs to mitigate this.