Add general wizard to generate shipping lables #6059
Made changes to label generation wizard. #6059

1. Removed on_change_carrier method which calculated shipping cost in
the initial wizard view.
2. Shipping costs are calculated anyway at the end state and are now
shown in the final view.
3. Attachments are shown in the final view itself.
4. Added tests for coverage.
5. Refactored wizard design.
Merge pull request #14 from PritishC/feature/task-6059

Made changes to the label generation wizard. #6059