Adds yam & config file

Closes #440 

Adds support for `.ember-cli` settings file which looks like this:

```json
{
  "port": 4200,
  "host": "0.0.0.0",
  "live-reload": true,
  "environment": "development"
}
```

By default, `ember-cli` is going to look for `.ember-cli` file in two places: the current directory and your home directory. You can put your personal settings in your home `.ember-cli` file, team shared settings should stay in project `.ember-cli`.
And if you look a few lines below, it will delete the file too.  This means that I cannot have a `~/.ember-cli` file while developing *on* the ember-cli project itself, but will have to manually recreate when I want to work on actual ember-cli applications (aka client projects).