Fix assets

move assets from assets/stylesheets/images to assets/images, fix logo in mailer template
The `host` is set, still I get a empty `src`:

```
> ActionMailer::Base.default_url_options
=> {:host=>"localhost:3000"}
```

Does `asset_url` work for you?

Also, I don't think that code you linked to actually works as expected:

```
> ActionMailer::Base.default_url_options
=> {:host=>"localhost:3000"}
> Errbit::Config.host
=> "errbit.example.com"
> (ActionMailer::Base.default_url_options ||= {}).tap do |default|
*   options_from_config = {  
*     host: Errbit::Config.host,    
*     port: Errbit::Config.port,    
*     protocol: Errbit::Config.protocol    
*   }.select { |k, v| v }    
*   
*   default.reverse_merge!(options_from_config)  
* end  
=> {:host=>"localhost:3000"}
```