Don't Require LineIcons

[sshaw]

One of the great things about this library is its size. Unfortunately it depends on LineIcons, whose CSS is larger that both this library's CSS and JS.

One can exclude LineIcons but then the X to close the banner is not visible. One must then add something like:

.lni-close::after {
    content: 'X';
}

I would be great to have defaults that don't require an external library.