Added intervals in StatisticsRecordedFragment with distance, speed and pace for all activity types.

Users can select the length of the interval (in a spinner with several options).
The intervals will be in km or mi depending on settings.

src/main/java/de/dennisguse/opentracks/viewmodels/IntervalStatistics.java

@@ -0,0 +1,67 @@
+package de.dennisguse.opentracks.viewmodels;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import de.dennisguse.opentracks.content.data.TrackPoint;
+import de.dennisguse.opentracks.util.LocationUtils;
+import de.dennisguse.opentracks.util.UnitConversions;
+
+public class IntervalStatistics {
+    List<Interval> intervalList;
+
+    public IntervalStatistics() {
+        intervalList = new ArrayList<>();
+    }
+
+    public void build(List<TrackPoint> trackPointList, float distanceInterval) {
+        intervalList = new ArrayList<>();
+
+        if (trackPointList == null || trackPointList.size() == 0) {
+            return;
+        }
+
+        Interval interval = new Interval();
+        for (int i = 1; i < trackPointList.size(); i++) {
+            TrackPoint prevTrackPoint = trackPointList.get(i - 1);
+            TrackPoint trackPoint = trackPointList.get(i);
+
+            if (LocationUtils.isValidLocation(trackPoint.getLocation()) && LocationUtils.isValidLocation(prevTrackPoint.getLocation())) {
+                interval.distance += prevTrackPoint.distanceTo(trackPoint);
+                interval.time += trackPoint.getTime() - prevTrackPoint.getTime();
+
+                if (interval.distance >= distanceInterval) {
+                    intervalList.add(interval);
+                    interval = new Interval();
+                }
+            }
+        }
+
+        if (interval.distance > 1f) {
+            intervalList.add(interval);
+        }
+    }
+
+    public List<Interval> getIntervalList() {
+        return intervalList;
+    }
+
+    public static class Interval {
+        float distance = 0f;
+        float time = 0f;
+
+        public float getDistance() {
+            return distance;
+        }
+
+        /**
+         * @return speed of the interval in m/s.
+         */
+        public float getSpeed() {
+            if (distance == 0f) {
+                return 0f;
+            }
+            return distance / (float) (time * UnitConversions.MS_TO_S);
+        }
+    }
+}