Hard-coded file names in German docs

[Michael Gerz]

Hartmut,

there are some hard-coded file names in the German user documentation. 
They won't work on other machines.

./de_Customization.lyx:
       filename 
/windows/D/EigeneDateien/LyX/Dokumentation/14x/images/layout-paragraph.xpm
       filename 
/windows/D/EigeneDateien/LyX/Dokumentation/14x/images/layout-paragraph.xpm
       filename 
/windows/D/EigeneDateien/LyX/Dokumentation/14x/images/layout-paragraph.xpm

./de_UserGuide.lyx:
       filename 
/windows/D/EigeneDateien/LyX/Dokumentation/14x/images/math/super.xpm
       filename 
/windows/D/EigeneDateien/LyX/Dokumentation/14x/images/math/sub.xpm

Michael