Previously when drop caps were specified in a paragraph style (not
as direct formatting) export to HTML was implemented with :first-letter
pseudo-class for "LibreOffice Writer" and through styling individual
characters for other browsers. Since all browsers used these days (even
obsolete ones like IE 5.5) support :first-letter there seems to be no
reason to maintain this difference. This patch unifies all export
modes to use :first-letter in such cases.