Improvements to reduce the number of incomplete applications

1. We've now added a Video and Audio Test window before starting an application. The test only shows when video responses are requested in the job post.

This should reduce the number of in-progress applications from candidates who start the application on devices without working cameras or microphones.

2. Incase a candidate comes back to the main application page - when they have an in-progress application, we now show them an option to resume the in-progress application instead of starting a new one.

This works only when the candidate visits the application page on the same browser/device combination used earlier.

This should reduce the in-progress/incomplete applications from candidates who keep coming back to the main application page.