Pretty up the SSL cert popover

Twitter makes use of green which is very feel good. It also shows the URL which is nice here since we don't have a URL Bar. Screenshot attached.

We should totally rip 'em off shamelessly because we're awesome like that.

Of course we should stick to the regular elementary alert layout here. So the icon should be 48px. Make sure we're using the correct padding. Primary text is bolder and "larger" with pango. https://elementary.io/docs/human-interface-guidelines#dialogs

There is a class "success" that should apply the green color. Let's go ahead and copy Twitter directly here and use it on the icon and the secondary text ;)