WISH: Direct link to recent live tracks for a specific user

[gwicke]

For safety purposes, it would be useful to provide a URL parameter that does the equivalent of filtering tracks to match only those of a specified user name. This would make it possible to share a flyxc URL as a tracking link to others, independent of tracking method used for any particular flight (e.g. xcontest live or inreach).

[gwicke]

As a side effect, such tracking links could also help introduce more pilots to flyxc.