Validate Swagger files when they are uploaded

[bajiat]

Definition of done

• Choose package for Swagger validation.
• Integrate the package to the project.
• Create a function to run the validation.
• Work with the developer working with issue to make sure the validation is run when a Swagger document is being uploaded.

[kyyberi]

https://www.npmjs.com/package/swagger-validate

[kyyberi]

https://github.com/BigstickCarpet/swagger-parser

[bajiat]

@frenchbread Are you already working on this? Did you have any PR's related to this?

[frenchbread]

@bajiat swagger file validation is not included in PR #517. Just host url modifications are done there.