Update average speed

ImportData.java

// Recalculate average speed
double previousspeed  =  (Double)torecord.getProperty("speed");
int previousoccurences =  (Integer)torecord.getProperty("occurences");
double currentspeed = analyzer.getHorizontalSpeed(track.getTrkpt(i).getTime());
double denormalizespeed = previousspeed * previousoccurences;
double newspeed = ((denormalizespeed + currentspeed) / (previousoccurences + 1));
// Update the data accordingly
torecord.setProperty("speed",newspeed);
torecord.setProperty("occurences",previousoccurences+1);