Openapi 2.0 (swagger) semantic validations

[eguzki]

Currently, toolbox validates swagger spec content at the following levels:

• yam/json syntax
• swagger schema

There are semantic validations not done to check, for instance, duplicated operationId, reported in issue #222

The following swagger spec passes current validation system of the toolbox, however it is not a valid swagger schema.

swagger: "2.0"
info:
  version: v1
  title: WebApplication1
host: localhost:3873
schemes:
- http
paths:
  /api/User:
    get:
      tags:
      - User
      operationId: User_Get
      consumes: []
      produces:
      - application/json
      - text/json
      - application/xml
      - text/xml
      responses:
        "200":
          description: OK
          schema:
            type: array
            items:
              type: string
  /api/User/{id}:
    get:
      tags:
      - User
      operationId: User_Get
      consumes: []
      produces:
      - application/json
      - text/json
      - application/xml
      - text/xml
      parameters:
      - name: id
        in: path
        required: true
        type: integer
        format: int32
      responses:
        "200":
          description: OK
          schema:
            type: string

Swagger spec makes it very clear that

Unique string used to identify the operation. 
The id MUST be unique among all operations described in the API. 
Tools and libraries MAY use the operationId to uniquely identify an operation, therefore, it is recommended to follow common programming naming conventions.

Semantic validations should be implemented to reject invalid swagger docs. Source for semantic validations: https://github.com/swagger-api/swagger-editor/tree/master/src/plugins/validate-semantic