Contentful-management

Changed
* Removed `SpacesUploadProxy` and simplified the logic to use `UploadProxy`. [52](https://github.com/contentful/contentful-management.py/issues/52)
* Updated `requests` version due to a vulnerability found in versions `2.19` and below.

As `RichText` moves from `alpha` to `beta`, we're treating this as a feature release.

Changed
* Renamed `StructuredText` to `RichText`.

Added
* Added support for `StructuredText` field type.

This release includes some minor-breaking changes. That said, those breaking changes are actually bug-fixes that actually match the behaviour of the SDK to
what's present in the README and the documentation.

Added
* Added missing `memberships` proxy on `Space`.
* Added `transformation` and `filters` to `Webhook`.
* Added `parameters` to `UIExtension.extension`.

Fixed
* Space Space Memberships Proxy now properly serializes attributes upon creation.
* Space Api Keys Proxy now properly serializes attributes upon creation.
* Environments Proxy now uses default behaviour.
* Space Roles Proxy now properly doesn't require a resource ID to be passed.
* Locales Proxy now properly doesn't require a resource ID to be passed.
* Space Webhooks Proxy now properly doesn't require a resource ID to be passed.

Fixed
* Fixes 422 error handling when no `name` or `path` attribute are sent in the error details. [36](https://github.com/contentful/contentful-management.py/issues/36)

Fixed
* Fixed Locale creation.