Fix paths to media in SVG files

- Fix a couple of full absolute paths, which are evil as they
are machine specific, impeding reproducibility.
- Use True™ filenames used on Wikimedia Commons
Add text list of file names

This text file holds the names and widths of the files necessary
to generate the presentation (one may use CommonsDownloader for that).
Add binary media files

Some of our files are taken from Wikimedia Commons, but are heavily
modified using another software, an operation which cannot be easily
reproduced. No choice but to commit the binary files for the presentation
to be compilable from scratch.
Add images section to ReadMe

We commited some files here, we must include the license.