Add additional mode icons for transit
@mlundblad
Submitted by Marcus Lundblad Link to original bug (#780953)
Description
As discussed during FOSDEM, we might want to add some additional icons for some specific "sub-modes". The most commonly seen one is propably "trolley bus", some others that could be nice is "tourist rail" (something like museum railways, could perhaps depict a steam loco). One novelty-escque one is "horse-drawn carrige" (which might be fun as a sort-of easer-egg like thing). The complete list of "hierarchical modes" can be seen in src/hvt.js