Sort is not stable when values are identical

[lyricnz]

When a table is sorted by a column where multiple rows have the same value, the order is not stable or predictable.

Normally refresh is slow enough that you might not notice this, but attached video demonstrates this with refresh triggered by mouse-move (unrelated patch). Ignore the silly colors :) The flickering rows each have price 3.23

https://user-images.githubusercontent.com/122371/137608338-3af860f3-9d7a-4939-8540-84487103097a.mov

[lyricnz]

There are 10 uses of sort.Slice() in the codebase - a couple of them may be vulnerable to unstable sorting.

favorites.go

    sort.Slice(sliced, func(i, j int) bool {
        return sliced[i].MarketCap > sliced[j].MarketCap
    })

portfolio.go

    sort.Slice(sliced, func(i, j int) bool {
        return sliced[i].Balance > sliced[j].Balance
    })

sort.go

    sort.Slice(list[:], func(i, j int) bool { 
        // switch depending on sortBy
    })

The video above is the third one.

[lyricnz]

Code could be changed to sort.SliceStable() but this relies on the current order of the items being predictable. Sometimes this might not matter, or perhaps we need to pre-sort by Rank?