Adds v-model support to dropzone files

[MatheusRich]

Fixes #441.

I've added a basic support to a v-model directive. So, given a object, we should be able to bind the files in dropzone like this:

files: {
  acceptedFiles: [...],
  rejectedFiles: [...],
  queuedFiles: [...],
  uploadingFiles: [...]
}

I've called updateFiles() after ALL dropzone events. I'm not sure about this, what do you think? Is there a better way to approach this? Tell me if there's something else to do (or if it has any bugs).

[MatheusRich]

Fixed the conflicts! I hope the stylesheet is correct. Is there any linter setted up?

[JohannesLichtenberger]

Any news on this?

[MatheusRich]

@JohannesLichtenberger It seems that this is not being maintained anymore. Check #473

[JohannesLichtenberger]

However, how to use https://github.com/Etheryte/vue-auto-dropzone with Nuxt.js? It doesn't support SSR as of now: window is not defined.