Add cursor line

[simurai]

Currently the gutter highlights the current line:

Question: Should instead the line in the editor be highlighted? That would match how the original theme is styled: http://ethanschoonover.com/solarized

[nstepien]

I think it should be a 1:1 port of the solarized theme, so 👍
People transitioning from a different text editor to Atom while keeping Solarized as their theme should feel right at home.
The color of the line number should be darker as well.

[schmty]

👍 I'm for it