Add basic SVG support (see #7108)
Handle SVG images in `File::__get('imageSize')`
Add support for SVG images with pixel-based dimensions
Use the "preserveAspectRatio" attribute to emulate image cropping
Make SVG files editable in the file manager
Create SVG thumbnails in the back end and make SVG files editable
Support `pt`, `em` and `%` in addition to `px`
Merge branch 'feature/svg' into develop