Adding combinedBody option to combine all body fields into req.body.

Currently when you specify multiple body parameters, req.body will get what's in the last textarea field. This change creates an option to take all body inputs and put them into a req.body object. For example:

--------------------
-Parameter-   -Value-   -Parameter Type-
Name:   [   John Doe   ]   body
Email:    [   jdoe@example.com   ]   body
--------------------

req.body will be:
'{"Name": "John Doe", "Email": "jdoe@example.com"}'

Without the combinedBody option req.body would be:
'jdoe@example.com'

It is enabled by specifying {combinedBody: true} in the SwaggerUi constructor.