tooltips improvements (#896)

* add and fix tooltips on toolbar

* move tooltips below buttons

* add global definition for tooltip hover over delay

client/src/components/categorical/category.js

@@ -169,7 +169,11 @@ class Category extends React.Component {
               )}
             </span>
           </div>
-          <Tooltip content="Use as color scale" position="bottom">
+          <Tooltip
+            content="Use as color scale"
+            position="bottom"
+            hoverOpenDelay={globals.tooltipHoverOpenDelay}
+          >
             <Button
               data-testclass="colorby"
               data-testid={`colorby-${metadataField}`}