Add bold property to BasicListItem
In network/kdeconnect-kde!259 (diffs, comment 46007), we thought that the default BasicListItem was too low-contrast for the items in kdeconnect-sms, which used to be bold and high-contrast but were now a bit hard on the eyes. This patch adds a "bold" property to BasicListItem which beefs up the font. Also increases the non-bold contrast of the subtitle font in the non-bold case.
Non-bold with old font opacity: