Improve datum-quality algorithm

[Gerzer]

The algorithm that determines whether a particular location datum is of high or low quality should be improved to take into account more information than just whether it was a user or a system GPS that reported a datum. This will also involve modifying the type field in the client-facing location API to be instead called quality with a value of either high or low.

This enhancement will cause a breaking change to the API, so the API version number should be incremented.

[mahi-pas]

I made a wiki for this, which you can read here