bugfix: in Googlemap service: calculate heading only if old position available
bugfix: createMarker() now creates the marker even if no position available for it
bugfix/refactoring: create the marker only if position available on the fly
create a random nickname of none available in local storage
better location tracking (retry on failures)
show the elapsed time in the last update col if suitable
refactoring and bug fixes: Googlemap.deinit()

release used ressources from google.Map in deinit()
don't create markers if the position from the device is not available
debug output removed
rename nickname function + minor tweaks

When user changes the nickname the old nickname will be deleted, so the same
user will not be registered twice after the renace operation

Additional map options (zoom factor and scale option) implemented