Better looking checkboxes (#3345)

Also showing icon only on hover on control headers

superset/assets/javascripts/components/InfoTooltipWithTrigger.jsx

@@ -9,15 +9,19 @@ const propTypes = {
   icon: PropTypes.string,
   className: PropTypes.string,
   onClick: PropTypes.func,
+  placement: PropTypes.string,
 };
 const defaultProps = {
-  icon: 'question-circle-o',
+  icon: 'info-circle',
+  className: 'text-muted',
+  placement: 'right',
 };
 
-export default function InfoTooltipWithTrigger({ label, tooltip, icon, className, onClick }) {
+export default function InfoTooltipWithTrigger({
+    label, tooltip, icon, className, onClick, placement }) {
   return (
     <OverlayTrigger
-      placement="right"
+      placement={placement}
       overlay={<Tooltip id={`${slugify(label)}-tooltip`}>{tooltip}</Tooltip>}
     >
       <i