Native: Allow files arrangement in multiple files

[sudeeptarlekar]

In legacy version of Chipmunk, while loading multiple files user can rearrange the order by dragging them around. This feature was missing from the NativeUI and this commit fixes that missing feature.

[sudeeptarlekar]

@AmmarAbouZor can you please review?

Thanks in advance :)

[AmmarAbouZor]

The changes are solid. However, I think we need to reconsider the decision to remove the color completely from source items and retrieve the color in render loop as items can go out of sync on multiple edge cases.

Like for now the if you disable one of the sources in the middle then the colors in segments in side view will not match the colors of items in the table (see snapshot)

I think saving the color with source items will keep the logic in one place. It would need to reassign the colors of sources on sort changes but it will keep the logic centered in one place instead of spreading the index logic everywhere and having to deal with edge-cases that we didn't count for