Creating objects returns instance of AdAccount

[thierryjacoel]

When using an AdAccount to create an object, such as a campaign, the returned object is an AdAccount where the fields are those of the created object.
eg:

const account = new AdAccount(ACCOUNT_ID);
account.createCampaign(
    ['id', 'name'],
    {
        'name': 'My Campaign',
        'status': 'ACTIVE',
    }
).then(campaign => {
    // do something with the campaign
});

Here the variable campaign is an AdAccount with its name set as My Campaign and its id being the id of the campaign created.

The returned object should be of the type of the object created.