Add delete mask button (Library 3)

[lukas-monet]

User story

1. As a user
2. I want to be able to delete the current selected mask
3. So that I am able to compute a video difference where the whole video is considered

Acceptance criteria

• right next to the file path upload button of the mask there should be a red "X" button
• the red "X" button should take around 10% of the width and the file path upload button should take around 90% of the width
• when clicking the "X" button the current selected mask should be deleted

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