Created DatePickerBtn and Started Using it in ProgressCreationScreen

Signed-off-by: Andreas Fahrecker <AndreasFahrecker@gmail.com>

lib/widgets/date_picker_btn.dart

@@ -0,0 +1,31 @@
+import 'package:flutter/material.dart';
+
+class DatePickerBtn extends StatelessWidget {
+  final String leadingString;
+  final DateTime pickedDate;
+  final void Function(DateTime) onDatePicked;
+
+  DatePickerBtn({
+    @required this.leadingString,
+    @required this.pickedDate,
+    @required this.onDatePicked,
+  }) : super();
+
+  @override
+  Widget build(BuildContext context) {
+    ThemeData appTheme = Theme.of(context);
+    return FlatButton(
+      onPressed: () async {
+        onDatePicked(await showDatePicker(
+          context: context,
+          initialDate: pickedDate,
+          firstDate: DateTime(1900),
+          lastDate: DateTime(2100),
+        ));
+      },
+      child: Text(
+          "$leadingString ${pickedDate.toLocal().toString().split(" ")[0]}"),
+      color: appTheme.accentColor,
+    );
+  }
+}