Sort exercises alphabetically in dropdown in vizualization tab (#210)

* Sort exercises alphabetically in dropdown in viz tab

* Linted code

lib/tabs/visualization.dart

@@ -49,10 +49,18 @@ class _VisualizationTabState extends State<VisualizationTab> {
         variables = await _dbHelper.getFitnessData();
       }
 
+      // fetch data from table
       final names = variables
           .map((entry) => entry['exercise'] as String)
           .toSet()
           .toList();
+
+      // sort names if not empty
+      if (!names.isEmpty) {
+        names.sort();
+      }
+
+      // update states
       setState(() {
         _exerciseNames = names;
         if (_selectedExercise != null) {