Office Import WMF files are of bad quality with a black background and a bad font display

This is reproducable at least on Linux.

When importing an Office document with a WMF file with small fonts, the imported image is of bad quality as they have a black background that should not be there.

This is linked to the fact that WMF export cannot work in OpenOffice headless mode and requires an X display to function. However JODConverter is not currently able to run Openoffice binded to an X display and since this also requires additional setup (an xvfb display).