Decide when and where to use icons in context menus

[hanaral]

I consistently feel like opening issues for context menu items that seem like good places to use colour icons - but then refrain from doing so not knowing the logic behind elementary's decision for using them in places like the AppCenter's dock icon (which isn't quite aligned right either)

Should they be exclusively used in context menus when they are a part of something like the rating widget in Music?

@cassidyjames