Fix non-zero thresholds

Time and distance thresholds are not compared to the location which caused the 'LocationUpdated' signal to be emitted the last time, but to the last 'below threshold' update. If consecutive location updates always have time or distance differences smaller than the threshold, the 'LocationUpdated' signal is never emitted again.

Save the location for which the 'LocationUpdated' signal was last emitted and compare new locations against it to determine whether to emit the signal or not.

EDIT: Removed the part which moved accuracy checks to service-client.