update `Spacegray` to support sidebar icons

Icons are from default / Soda / a download from a user of the sublime text
forum.

Note: My Sublime Text messed up with tabs and spaces (at least I think so), but the only things I've changed are starting after the "sidebar group open" ending before "STANDARD TEXT BUTTONS". The 3 groups on the very bottom to "fix" an issue were removed as well.