Add subtle edit button to instructions bar

[greenberga]

Closes #1396

[outoftime]

@greenberga nice! a few thoughts………

1. Maybe less than 100% opacity?
2. Maybe only do the hover thing if the bar is open?
3. Maybe move the edit button to the bottom of the bar?
4. The bar width changes slightly between edit and normal mode (i think the edit icon is pushing it out a bit) which will surely drive me mad
5. A linter error : )

[greenberga]

I had actually meant to bring up the changing bar width! Seems like I didn't have to though 🙂 Any idea what might be causing that? It's weird because the characters seem to have the same width...

All good ideas! Will get to implementing them.

[outoftime]

@greenberga soooo weirdly now I can’t repro the width changing!? even though i still have the same commit checked out…

anywho, also occurred to me that a quick transition on the opacity (fade in/out) would be nice ; )

[greenberga]

I can still reproduce the changing width in Firefox...I wonder if it's just because the icon is a different size? Let me try switching icons and see if that fixes it.

[greenberga]

@outoftime okay, I think I did all the things! Would you mind taking another look when you have the time?

[outoftime]

Very good!