You can use the directories view to manually browse media files.
As for the categorization/etc, that information is pulled from the metadata stored in the media files themselves. You can use software like EasyTAG to fix the metadata.
For the longest time SVGs were not legal drawables files - usually they had to be SVG files. Although it was apparently announced at Google I/O that SVG will now be supported, but that is only in very recent Android versions.