Extend marketplace with actions and schemas

[chriskapp]

Currently our marketplace allows to install apps. We should think about extending the marketplace with actions and schemas. This would mean that a user can download pre-configured actions and schemas into the Fusio instance. We could add a marketplace button at the action and schema panel where the user can browse and install actions and schemas.

On the other side we could also provide a way for users to submit an action or schema to the marketplace.