CoverImage plugin: add "Size and background" options (#6884)
CoverImage plugin: add "Size and background" options (#6884)


NiLuJe/koreader,Frenzie/koreader,pazos/koreader,mwoz123/koreader,poire-z/koreader,Markismus/koreader,poire-z/koreader,koreader/koreader,Hzj-jie/koreader,Frenzie/koreader,NiLuJe/koreader,koreader/koreader