Tacklog gps subscription bugfix v1.8.35

Tracklog recording was failing because of the foreground service's async update and stop methods. Changed the notification refreshing logic in the GPSHandler, and made the service calls more synchronous with await.

this fixes issues #160 (closed) #162 (closed) hopefully.

Tracklogs timestamps are formatted to isoString when exporting it into GPX format #171 (closed)

Session id will be uploaded with the tracklog if exists. #173 (closed)