Add the ability to also change front page theme

Problem/Motivation

Exactly what I need, thx - except one thing: it is not possible to change the theme for (only) the front page (or am I missing something?)

Proposed resolution

Add a check wheter the path "/" is configured to use a different theme in PathThemeNegotiator.php :

if (!array_key_exists('/', $paths) && $pathMatcher->isFrontPage()) {