fix Kwf namespace initialisation

might be not yet set in frontend
Add dynamic padding-bottom as placeholder for image
Add "dont-hash-type" option to kwf-media-url
Provide image at correct size. Change image when changing size.
Only return defined sizes of image, not every pixel-width
Remove dpr2 stuff
Move calculations into template-vars
Improve Events for media-cache delete, add test
Introduce and use getBaseImageUrl function, update tests
Set correct min and maxWidth for different components depending on steps
Add isValidImage check to return invalid if dh-WIDTH should not be existent
Set correct image-width in imageUrl
Improve js to only add one img-tag
Fix tests