CommandHandler: Call the SimpleCommandService/onCommandEvent listener di...

… directly so that plugins registering commands via the dispatcher get the command.

This is more to discuss, but it works so feel free to merge anyway if you think this is okay.

Sponge's SimpleCommandService [listens for CommandEvent](https://github.com/SpongePowered/SpongeAPI/blob/master/src/main/java/org/spongepowered/api/service/command/SimpleCommandService.java#L73) but *how should this be registered*?

The event manager requires a valid plugin instance, so should the Granite server be an implicit plugin by itself?

Right now it's just calling that event handler directly which works but is of course a *bit* of a hack :grin: