Bug: cannot remove container configuration

[aistis-]

Once an app is created on Marathon with container configuration, it is not possible to remove container configuration without recreating the app.

• GUI JSON mode: removing container key or setting container: null does not remove container configuration
• GUI leaving all container fields empty results error /container: must not be empty
• API: PATCH and PUT without container key or sending container: null does not remove container configuration
• API: PATCH and PUT sending with empty container values gives error that docker config is missing