Add error-formatter component to parse and display adapter errors

[begedin]

This will close #85 and possibly #28 and #29

The phantomjs installation ember-cli includes in its locally installed npm package somehow got corrupted on my end, causing the browser to crash while running tests.

To get around it, I deleted the node_modules folder and re-ran npm install. I'm guessing some components got updated this way, due to how we specify our versions, so as a result, the default message an AdapterError contains changed, causing tests to fail.

Since we already talked about formatting errors such as that one in a nicer way, I decided to quickly implement an error formatter component, to use in place of these basic errors.

An adapter error looks like something along the lines of

errors: [
  // contains errors returned by the API. In case of validation errors, there will be multiple
  // in case of a generic error, there will usually be just one object
  { 
    id: 'ERROR_ID'
    title: 'Error title',
    detail: 'error detail', },
    status: 404 // status code,
    // this last one is only for validation errors
    source: { pointer: 'data/attributes/field_with_validation_error' }
  }
],
message: 'Some sort of standard error message goes here'
// there are other properties here to, but of no concern to us at the moment

For each error in the errors array, the component will output a

<p class="error">{{error.title}}: {{error.message}}</p>

I think that's sufficient for now, but we will be able to modify this behavior as we please in the future.

[begedin]

@joshsmith The tests actually failed on CircleCI as well, with the same PhantomJS crashing issue. I had to "rebuild without cache" to get them to run.

We may have a different problem here, but I'm not sure what it could be.