GNSS improvments: - Introduce alive indicator; Status string will switch between white and grey with every message received from the module - shorten visibility of "shutting down" string. a busy wait of 1 second was applied in the sleep prepare function. The time is now included in the time needed to prepare the module for low power operation - make sure GPIO is properly initialized after deep sleep

Heinrichs Weikamp OSTC4 update files.

The builds are for testing purposes only. Be careful, they might not work and are definitely not recommended for real dives.