ImageViewPage: Make thumbnail bar a proper ToolBar with better centering behaviour
Use proper toolbar styling with the complementary colour set to properly frame the view. Centering behaviour is amended to keep the item in the center and survive width changes due to animations and window resizing.
I do not believe it is possible to have a horizontal scroll bar without compromising the look and feel, due to highlight centering behaviour. I think this is fine as a user can go back if they want to look for specific media.