Add "navigate to" for the starting point of future events

[etabakov]

When attending an event on a place for the first time, it could be hard to find the starting location, especially for the XLruns. We can add an option to "navigate to" the starting point easily from the list with future events. It can fallback to the installed navigating maps with prefilling the geoposition of the starting point.

One neat package that can help with this: https://pub.dev/packages/maps_launcher

In addition, we need to create some lightweight backend that maps location with geolocation of the starting point. This could be in Firebase for simplicity.