Add the ability to compare differences between levels

In the level select screen, there should be a button that says Compare Levels. That button will take you to a screen where you can select two different levels. The differences will be shown with a split screen with buttons similar to the ones in the search results of the Search function, except with the differences clearly highlighted in blue, I guess (blue text isn't really used elsewhere in Ved), and the buttons won't be aligned in a single vertical list, but instead will be spread out everywhere.