Icon styles are inconsistent

Sometimes we use colorful, shaded style icons:


Other times we use "modern" flat, single color icons:


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For reference, Ida uses the former approach:


Some tools like PyCharm use flat icons, sometimes with color:


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Personally I don't have a strong feeling one way or the other, but we should pick a style and be consistent. The latter approach has the benefit of using font-based icon sets which have many usable ones ready to go and we don't have to worry too much about design.