Inconsistency of symbolic links; create them on buildtime

I'd like to make a suggestion.
I noticed that there are symbolic links in some sizes, which are not in there in other sizes, e.g. there is a symbolic link `apps/16/calendar.svg` but not `apps/24/calendar.svg`.

My suggestion would be to make a list for symbolic links, something like
```
image-x-generic.png <- image.png
image-x-xcf.png <- image-x-compressed-xcf.png
internet-feed.png <- application-atom+xml.png
internet-feed.png <- application-rss+xml.png
model.png <- application-x-blender.png
model.png <- image-x-3ds.png
office-contact.png <- text-directory.png
office-contact.png <- vcard.png
package-x-generic.png <- package.png
```
and create the symbolic links on build time. This includes to remove the symbolic links from the repo and just keep the actual svg files, which will make everything look clearer (also no more vacuum svg files, if you only add symbolic links -> cleaner git history).