Create the home screen of the app.
Create a ListView for the Categories.
Fill out the TODOs in main.dart and category_route.dart using the specs below.
If you had customized your category.dart, you can replace our category.dart with yours.
Customize your app if desired. Some ideas are listed below.
The AppBar text should say 'Unit Converter' with a font size of 30.0, and an elevation of 0.0.
A list of 8 Categories should be shown on the screen. You should be able to scroll down the list. There should be 8.0 horizontal padding around this list.
The AppBar and app body should be the same color. In our example, we use Colors.green[100].
