Have mix kitto.server in :dev env watch assets
Have mix kitto.server in :dev env watch assets

Instead of having the user start webpack-dev-server using another shell
instance, we have the kitto.server task start it.
Configuration:

Specify a different asset watcher, or different options to webpack:

```elixir
config :kitto, :watcher, grunt: [bin: "relative-path-to-grunt-bin",
                                 opts: ["option1", "option2"]]
```

kittoframework/kitto,kittoframework/kitto