Added custom animations and custom width options

Hi there,

I've added some custom animation options. With this you can implement your own animations and not the default slideDown stuff.

Also I've added the option to set a custom width if you need to.

To get this stuff via bower I've added the components.json. I think you might add this by yourself:
```bower register backbone.bootstrap-modal git://github.com/powmedia/backbone.bootstrap-modal```

Feel free to accept this or reject it. If rejected, please tell what I have to do to get this stuff into the plugin.

Greetings Kersten