Add GPSTrackerDemo (#9)

[XandrMaster]

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Description

Please list all relevant dependencies in this section and provide summary of the change, motivation and context.

Fixes # (issue)

Type of change

• [ ] Bugfix
• [ ] Feature

Checklist

• [ ] I have read the contribution guide: https://vaadin.com/docs/latest/guide/contributing/overview/
• [ ] I have added a description following the guideline.
• [ ] The issue is created in the corresponding repository and I have referenced it.
• [ ] I have added tests to ensure my change is effective and works as intended.
• [ ] New and existing tests are passing locally with my change.
• [ ] I have performed self-review and corrected misspellings.

Additional for Feature type of change

• [ ] Enhancement / new feature was discussed in a corresponding GitHub issue and Acceptance Criteria were created.

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[Legioth]

Sorry for missing this PR. It seems like the application is no longer deployed at that URL so I'm closing this. You can make a new PR if the app is deployed somewhere else or if it was just a temporary glitch with the deployment.