Qt/MemoryViewWidget: Replace the click-to-center behavior with a scrollbar.

[AdmiralCurtiss]

More refactoring of this thing to make it more usable.

User-facing changes:

• Removes the (imo infuriating) behavior that clicking anywhere in the table centers the table on that row.
• Instead adds a scrollbar that can be used to navigate the view.

Keyboard keys (up/down/pageup/pagedown) can still be used like before, no major change there yet -- though they do now respect the bytes per row, which they didn't before.

Internal changes:
The table is now a member of the MemoryViewWidget rather than the widget itself. This was necessary because I made a custom scrollbar that can deal with the infinitely-long memory view (since it wraps around), and attached that to the side of the memory table but still handle it as part of the MemoryViewWidget. The scrollbar always jumps back to the center after every interaction with it, and when dragging only has a limited range until you let go and re-grab it. I think this is pretty intuitive considering what we're dealing with here, but ymmv.

[Tilka]

Do you want to do the code view next? :)

[AdmiralCurtiss]

That's probably a good idea, yes.