`userListItem.jsx`: Listen to event fired by "i" button (which toggles details); Fire event to toggle buttons from bottom to top

`heroes.jsx`: Move `.round-buttons` up in DOM; Fire & listen to event to keep track of which "card" is current; Revert buttons to bottom when changing "cards"; Fire event to link "i" button to current "card"; Removing unused code

`app.scss`: Adding `.round-buttons.top` state; Minor CSS changes related to moving `.round-buttons` up in DOM