Add lilypond-flow images

Add image files for the lilypond-flow display on "Text input".

- Add small and fullsize png files for English and German
- Add PDF files for English and German  
  (is it possible to use png for the website and pdf for pdf manuals?)
- Add tex source(s) used to generate the images  
  I suggest adding a picture-src folder for such sources  
  (if I didn't get something completely wrong)
- Add a script to process the .tex file (or a translation)