Resolve "Avoid print calls in production code"

Closes #77 (closed)

lib/utils/random_pick_grid.dart

 import 'dart:convert';
+
 import 'package:flutter/services.dart';
 
+import 'package:sudoku/utils/tools.dart';
+
 class RandomPickGrid {
   RandomPickGrid();
 
@@ -19,12 +22,12 @@ class RandomPickGrid {
       final jsonResponse = await json.decode(jsonString);
       grids = jsonResponse['templates'][size][level];
     } catch (e) {
-      print("$e");
+      printlog("$e");
     }
 
     // Check we have enough grids
     if (grids.isEmpty) {
-      print('Not enough grids [$size, $level] in templates.');
+      printlog('Not enough grids [$size, $level] in templates.');
     }
 
     // Randomize grids list