Inspection to simplify multi-mapping mapping files to single ones

[picimako]

Summary

In stub mapping files, where only a single request-response mapping is defined within the mappings property can be simplified by unwrapping the mapping and removing the mappings property.

Tasks

• Create an inspection that can detect mappings properties with a single request-response mapping.
  • What about cases when the children look like this: request-response, response, request, none?
• Add quick fix to remove the mappings property like this:

  
  //from
  {
  "mappings": [
  {
     "request": { ... },
     "response" : { ... }
  }
  ]
  }

//to { "request": { ... }, "response" : { ... } }

- Make sure to keep any other properties specified.
- In case there is a `meta` property specified as well, besides `mappings`, don't report anything, because the meta might contain important properties that can be lost if users are not cautious enough when using the quick fix.

## To be clarified
- Look into other properties if they need special care.

[picimako]

Completed in v1.0.6.