Add a speed gate to determine whether to replace the current location with a less accurate one

Currently, locator allows replacing a more accurate location with a less accurate one as long as the old location lies outside the new location accuracy circle.

For me, this results in jumps between a precise GPS location and a hugely inaccurate, province-wide MLS-determined location around 300 km away.

This change adds a maximum speed gate of 500 meters per second to determine whether the new location is plausible and virtually eliminates these jumps.

To handle cases like people getting off a plane thousands of kilometers from their last location there is also age of the previous location criterion - if the previous location was determined more than 30 minutes ago then the speed gate is not enforced. 30 minutes is an equivalent of a 900 km distance at that speed.

This change does not have any impact on replacing the current location with a more accurate one - this is always allowed.