Contentful-management

Added
* Added Organizations Endpoint.
* Added Webhook Calls and Health Endpoints.
* Added Content Type Snapshots Endpoints.
* Added UI Extensions Endpoints.
* Added Personal Access Tokens Endpoints.
* Added Users Endpoint.
* Added Space Memberships Endpoints.

Fixed
* Fixed `Accept-Encoding` header when `gzip` was disabled.
* Fixed docstrings.
* Fixed Content Type Field IDs not being correctly serialized [17](https://github.com/contentful/contentful-management.py/issues/17)

Added
* Added `Array` wrapper [13](https://github.com/contentful/contentful-management.py/issues/13)

Fixed
* Fixed issue when calling `to_json()` on entries with new fields added [10](https://github.com/contentful/contentful-management.py/issues/10)

Added
* Added `X-Contentful-User-Agent` header for more information.

Added

* Added check for undefined fields from the WebApp against presence in the Content Type

Fixed

* Fixed VersionMismatch parsing error [2](https://github.com/contentful/contentful-management.py/issues/2)

Changed

* Reuse result from `publish` for reloading [1](https://github.com/contentful/contentful-management.py/issues/1)

* Add `snapshot` property to Snapshot API.