add class and id customization

Added class and id customization, I wasn't sure if it would be a good idea to let any attribute be added trough attr-, so I used an object to define allowed attrs and defaults.

I decided to use the attr- prefix to prevent adding double classes and ids.

Usage example:

    <autocomplete 
        attr-placeholder="some placeholder" 
        attr-class="your-custom-class" 
        attr-id="your-custom-id" 
        click-activation="true" 
        data="movies" 
        on-type="doSomething">
    </autocomplete>

Probably a fix for #3