Show loading spinner while frame differences are computed (Library 3)

[lukas-monet]

User story

1. As a user
2. I want to see a loading spinner while the frame differences are computed
3. So that I know that the software is still doing something

Acceptance criteria

• after clicking on the button: "Compute and Display Diferences" a loading spinner should be shown as long as the computation takes
• below the loading spinner there should be a 'X'
• when clicking the 'X' the computation gets canceled
• while the loading spinner is active the background should be inactive and darker
• the loading spinner should look similar to this:
  
• when the computation is finished and the program jumps to the video player screen the loading spinner should disappear

Definition of done (DoD)

• Create feature branch
• Implement the functionality
• Opened pull request and assigned reviewer
• If necessary: required changes are implemented
• Delete feature branch
• If necessary: Component Test has been written
• Code review has been completed and code has been merged

DoD general criteria

• Feature has been fully implemented
• Feature has been merged into the mainline
• All acceptance criteria were met
• Product owner approved features
• All tests are passing
• Developers agreed to release