Added an option to skip response formatting in Content/Admin API SDKs

[phawazzzy]

closes #73

• Added formatResponse option to the parameter that would be passed in the GhostAdminApi/GhostContentAPi
  -the formatResponse is default to true when not specified by consumer

This how it would look like
const api = new GhostContentAPI({
url: 'YOUR URL',
key: 'YOUR KEY',
version: "VERSION",
formatResponse: true/false
})

• [x ] There's a clear use-case for this code change
• [ x] Commit message has a short title & references relevant issues
• [ x] The build will pass (run yarn test and yarn lint)

[Robogeek95]

This presents an option to skip formatting the returned response from the api