Look at Kalman filtering to reduce GPS noise

Especially important for lower quality phones, but this can quite dramatically reduce noise even in fairly open skies on an iPhone! See https://mastodon.social/@_Davidsmith/111409340172869799.

This can be added to the `NavigationController` and be applied transparently. Probably should be configurable in case someone wants to disable it.

Start by reading the NavigationController and the issue's linked Kalman-filtering reference. Determine how GPS locations enter the controller and where configuration is exposed; done should mean reduced GPS noise on lower-quality phones while allowing users to disable the filtering.

Written by the indexing model from the issue text.