FEATURE: Omit srcset and sizes if imageSource is non-scalable

[manuelmeister]

Since size attribues for non scalable sources like svg files are pointless they should be avoided.
This change ensures that only scalable imageSources will render size and srcset.

[mficzel]

Makes total sense. It would be great to only have the changes in Image.fusion and Source.fusion ... i will take care of any linter issues.

[mficzel]

Will adjust myself during rebase

[manuelmeister]

Thanks! Why did you revert adc8066#diff-0eb29729c0c4c6990f6489cbff5970dd109c7362d6813d70e95cdbb002031dabR233 the return null? I think it is wrong to return the src in the srcset function.

Sitegeist.Kaleidoscope/Classes/Domain/AbstractImageSource.php

Line 233 in 3c95847

return $this->src();