Improve UI for empty /lists state

[ttntm]

Hi there,

just a suggestion for the "no lists" (=empty) state of the /lists route.

It's not looking quite alright the way it is, i.e. displaying that gray line above the "create list" mini-form:

Mobile and small screens look alright, they display a heading with an icon. It's really just the bigger viewports that make this look weird somehow.

Suggestions:

1. Remove that gray line, keeping the "add list" form in the same line as the "search" input
2. Display some "You don't have any lists yet..." text above the line, so it makes more sense and gives a feeling for the intended UI