Tests for createlink bugs

Inserting link currently *fails* reliably on `BROWSER_NAME='firefox' BROWSER_VERSION='29' PLATFORM='WINDOWS' ` 
If that’s what the big applications do, I think it would be good for us to do it!

This sort of thing isn't a patch, so I think it belongs as a Scribe command instead of a Scribe command patch (this is just an infrastructure we have for separating concerns in our code). Here are some examples of Scribe commands: https://github.com/guardian/scribe/tree/master/src/plugins/core/commands

Your command patch’s `execute` method will be invoked by your command’s `execute` method.

``` js
execute: function (value) {
  scribe.api.Command.prototype.execute.call(this, value);

  selection.selection.collapseToEnd();
}
```