added proxy server option

Moving this https://github.com/divshot/divshot-cli/issues/116 discussion here.

I've added the proxy settings to most of them. And I started to use the cli app from start and now I'm stuck on `push`. Same issue with conn refused coming from this line:

```js
cli.api.apps.id(config.name).builds.create({config: config}, function(err, build){
```

in `push.js` file.