Add a background to the tooltip label so long strings also have background
Add a background to the tooltip label so long strings also have background

Contributes to #57

ad1217/Cura,fieldOfView/Cura,ynotstartups/Wanhao,ad1217/Cura,markwal/Cura,quillford/Cura,totalretribution/Cura,Curahelper/Cura,quillford/Cura,senttech/Cura,lo0ol/Ultimaker-Cura,fieldOfView/Cura,markwal/Cura,fxtentacle/Cura,hmflash/Cura,DeskboxBrazil/Cura,fxtentacle/Cura,bq/Ultimaker-Cura,senttech/Cura,lo0ol/Ultimaker-Cura,bq/Ultimaker-Cura,totalretribution/Cura,DeskboxBrazil/Cura,ynotstartups/Wanhao,Curahelper/Cura,hmflash/Cura