Statistics/graphs section implemented

Only using sample data atm

lib/common/widgets/charts/grouped_bar_chart.dart

@@ -0,0 +1,81 @@
+/// Bar chart example
+import 'package:flutter/material.dart';
+import 'package:charts_flutter/flutter.dart' as charts;
+
+class GroupedBarChart extends StatelessWidget {
+  final List<charts.Series> seriesList;
+  final bool animate;
+
+  GroupedBarChart(this.seriesList, {this.animate});
+
+  factory GroupedBarChart.withSampleData() {
+    return new GroupedBarChart(
+      _createSampleData(),
+      // Disable animations for image tests.
+      animate: false,
+    );
+  }
+
+
+  @override
+  Widget build(BuildContext context) {
+    return new charts.BarChart(
+      seriesList,
+      animate: animate,
+      barGroupingType: charts.BarGroupingType.grouped,
+    );
+  }
+
+  /// Create series list with multiple series
+  static List<charts.Series<OrdinalSales, String>> _createSampleData() {
+    final desktopSalesData = [
+      new OrdinalSales('2014', 5),
+      new OrdinalSales('2015', 25),
+      new OrdinalSales('2016', 100),
+      new OrdinalSales('2017', 75),
+    ];
+
+    final tabletSalesData = [
+      new OrdinalSales('2014', 25),
+      new OrdinalSales('2015', 50),
+      new OrdinalSales('2016', 10),
+      new OrdinalSales('2017', 20),
+    ];
+
+    final mobileSalesData = [
+      new OrdinalSales('2014', 10),
+      new OrdinalSales('2015', 15),
+      new OrdinalSales('2016', 50),
+      new OrdinalSales('2017', 45),
+    ];
+
+    return [
+      new charts.Series<OrdinalSales, String>(
+        id: 'Desktop',
+        domainFn: (OrdinalSales sales, _) => sales.year,
+        measureFn: (OrdinalSales sales, _) => sales.sales,
+        data: desktopSalesData,
+      ),
+      new charts.Series<OrdinalSales, String>(
+        id: 'Tablet',
+        domainFn: (OrdinalSales sales, _) => sales.year,
+        measureFn: (OrdinalSales sales, _) => sales.sales,
+        data: tabletSalesData,
+      ),
+      new charts.Series<OrdinalSales, String>(
+        id: 'Mobile',
+        domainFn: (OrdinalSales sales, _) => sales.year,
+        measureFn: (OrdinalSales sales, _) => sales.sales,
+        data: mobileSalesData,
+      ),
+    ];
+  }
+}
+
+/// Sample ordinal data type.
+class OrdinalSales {
+  final String year;
+  final int sales;
+
+  OrdinalSales(this.year, this.sales);
+}