Reset habit strength graph scroll location when switching scale

- Create ScrollableChart.reset() to set x coordinate of scroller
- Call reset() from doInBackground() in ScoreCard to reset scroll location

android/uhabits-android/src/main/java/org/isoron/uhabits/activities/common/views/ScrollableChart.java

@@ -217,6 +217,13 @@ public abstract class ScrollableChart extends View
         scrollController = new ScrollController() {};
     }
 
+    public void reset()
+    {
+        scroller.setFinalX(0);
+        scroller.computeScrollOffset();
+        updateDataOffset();
+    }
+
     private void updateDataOffset()
     {
         int newDataOffset = scroller.getCurrX() / scrollerBucketSize;

android/uhabits-android/src/main/java/org/isoron/uhabits/activities/habits/show/views/ScoreCard.java

@@ -153,6 +153,7 @@ public class ScoreCard extends HabitCard
             else scores = scoreList.groupBy(getTruncateField(bucketSize), firstWeekday);
 
             chart.setScores(scores);
+            chart.reset();
             chart.setBucketSize(bucketSize);
         }