standalone LaTeX package that is being used now doesn't work on openSuse and maybe on some other distributions. This patch makes the latex renderer using the preview package. Setting the background and the font colors as well as the font size works well.

One remaining issues is the white document margin line which becomes visible when using dark desktop theme (=dark colors in Cantor's worksheet). This minor issue will be addressed in another fix, if a solution for this problem is possible. If not, we should still go for this patch since it's better to accept think bounding box around formulas with dark themes on openSuse than accepting completely broken Cantor worksheet on this distribution.