editable menu color on mobile

[alishaevn]

story

on the mobile view of the webstore, the menu button (3 lines) is always set to black. this should be editable so that apps with a dark colored header don't interfere with being able to see the menu button. (we're already able to change the color of the header links. we may be able to extend that color to the menu button as well).

acceptance criteria

• the mobile menu color is editable per application

demo

[alishaevn]

the menu button on mobile uses a background-image property, so it can't be changed by simply updating the color style.