theme: add bar-separator-width setting

src/config/handler.rs

@@ -2399,6 +2399,7 @@ impl ConfigProxyHandler {
             TITLE_HEIGHT => ThemeSized::title_height,
             BORDER_WIDTH => ThemeSized::border_width,
             BAR_HEIGHT => ThemeSized::bar_height,
+            BAR_SEPARATOR_WIDTH => ThemeSized::bar_separator_width,
             _ => return Err(CphError::UnknownSized(sized.0)),
         };
         Ok(sized)