Add W'bal Time In Zone (3a of 3c)

.. add W'bal distribution to Histogram
   - for a ride
   - for a date range
   - for a compared ride
   - for a compared date range

.. still need to revisit to do in zones (3b)

.. still need to update ridesummary to show
   summary of w'bal zone distribution (3c)

src/RideFileCache.cpp

@@ -1368,9 +1368,6 @@ RideFileCache::computeDistribution(QVector<float> &array, RideFile::SeriesType s
             else wbalTimeInZone[3]++;
         }
 
-        // turn array into percents (TiZ stays in seconds)
-        for(int i=0; i<100; i++) array[i] = array[i] / double(count) * 100.0f;
-
     } else {
 
         foreach(RideFilePoint *dp, ride->dataPoints()) {