Add support for absolute imports to import/order

Currently, when you have the [order](https://github.com/benmosher/eslint-plugin-import/blob/master/docs/rules/order.md) rule turned on and the option `newlines-between` set to `always`
it will give errors when you have something like this:

``` js
import a from '/imports/config';
import b from '/imports/some/folder'
```

This will report having an empty line between the imports which in my opinion isn't correct.
### Proposal

Add a new string to the order rule called `absolute`.

Start with the linked import/order rule documentation and inspect how `newlines-between` handles the absolute import examples. Define the behavior of the proposed `absolute` order option, then verify that enabling it no longer reports the shown imports as requiring an empty line.

Written by the indexing model from the issue text.