Change widgets file format from .png to .svg

**Describe the bug**
Widgets "Big status badge", "Small status badge" and "Panel" are not generated in `svg` format.
This is a general issue!

**To Reproduce**
1. Go to 'https://hosted.weblate.org/widgets/weblate/'
2. Click on the "Big status badge", "Small status badge" or "Panel" widget
3. Scroll down to 'HTML code'
4. See file extension ".png"

**Expected behavior**
All widgets should be generated in `svg` format.

**Additional context**
This may be just my own preference, but IMO, `svg` is a widely used and supported format nowadays. The format supports image scalability as well as text searchability. IMO, pixel-based png files are not ideal.
Take a look at https://planner-todo.web.app/, scroll down to the section **Use Planner in your Language**. The widget displays pixelated.

**Conclusion**
If there is no specific reason for the `png` format, I'd sudgest to change all widgets to `svg` format.