[Feature request] allow to import and navigate gpx files from Route preparation

[katerynakocherhina]

Before you can navigate a .gpx track you first have to import the .gpx file into the app's database. Only when the track is imported into the database you can select it to navigate. It would be convenient to select a .gpx file from the smartphone's file system (if it is already imported into the device storage folder) and just start it.

[tbertels]

Specifically, you have to open the .gpx file, open navigation, options, follow track, select the track, select "start of the track", close, and then you can start the navigation.