[FE] Improve usability to validate PDF with other settings.

[yuliya-ivaniukovich]

We need to upload PDF every time instead going back to settings page

[yuliya-ivaniukovich]

We are making this for the users, not for testers. For the user it's not a common use case to validate PDF file one more time. Moreover we are going to make settings page optional because most of the users won't need it.

However in rare cases it's indeed could be useful to re-validate the same file. I propose to use browser's back button. If more evident solution is needed we can consider making 'Validate another file' button as split button where in dropdown there will be another option to 'Validate same file again'.
@bdoubrov could you please clarify with Han this question when we start Milestone 2 officially.