Renamed show methods to be more intuitive

Minor change. Just a refactor, no logic change.

```objc
// show the panels
- (void)showLeftPanelAnimated:(BOOL)animated;
- (void)showRightPanelAnimated:(BOOL)animated;
- (void)showCenterPanelAnimated:(BOOL)animated;
```

Reason being I nearly created more methods to choose whether or not to animate the changes. I assumed the <code>BOOL</code> was for choosing whether to show or hide the panels.