Add support for Garmin Fenix 5x base

[slavitch]

Add support for Garmin 5x

(if supported doesn't show up in Garmin store)

[grigorye]

Just to keep you in the loop: I'm still considering adding support for Fenix 5x and the likes, while working on the next version of the app. The main challenge there is lack of APIs for background operation (in the firmware), but that's something that may become less critical with the improvements introduced in the next version. Hence, it won't be part of v2 of the app, but there's still a chance that it could be addressed later.