Investigate usage of SVG images instead of PNG

**What is the current behaviour and why should it be changed?**

Currently we mainly use png images (even in places where vector based images would be beneficial) . We should discuss if we want to move to SVG instead. This has the advantage of a potentially smaller app, easier size modification. However it's more complex to render them.

**Describe possible approaches**

Convert new images to SVG. This might introduce a new Qt dependency.

@jamulussoftware/designers I assume you're already working on the new instrument set in SVG format?

**Has this feature been discussed and generally agreed?**

No. However see: https://github.com/jamulussoftware/jamulus/pull/2508

Start by reviewing the current PNG image usage in Jamulus and the related pull request #2508. Investigate whether SVG rendering would require a Qt dependency and document an agreed approach for converting new images or adopting SVG more broadly.

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