Fix remoting metadata for "data" arguments [2.x]

[bajtos]

Fix the definition of "data" argument to

{ type: 'object', model: modelName, ... }

That way strong-remoting passed the request body directly to the model
method (does not create a new model instance), but the swagger will
still provide correct schema for these arguments.

This fixes a bug where upsert in relation methods was adding default
property values to request payload.

Connect to #1806
Requires also strongloop/loopback-swagger#55 to be released around the same time

@0candy please review

This patch clashes with #2539 which is in review too. We need to rebase the second patch to be landed after the first one is merged.

[0candy]

@bajtos The code change LGTM. But does this code need to be in 3.x?

[bajtos]

But does this code need to be in 3.x?

I'll forward-port to 3.x later. I started with a patch sent against 2.x to see how downstream dependencies are handling the change. There are very few dependents using LooBack 3.x. It has happened to us very recently that we landed a patch to 3.x because all looked well and then there was a bunch failures after back-porting to 2.x

[bajtos]

I compared swagger documents produced before this patch and after this patch. The only difference is that with this patch in place, the responses for relation methods include the description from remoting metadata, which is a good thing IMO.

(...)
@@ -267,6 +270,7 @@
           description: Model instance data
           required: false
           schema:
+            description: Model instance data
             $ref: '#/definitions/Category'
       responses:
         '200':
@@ -373,6 +377,7 @@
           description: An object of model property name/value pairs
           required: false
           schema:
+            description: An object of model property name/value pairs
             $ref: '#/definitions/Category'
         - name: id
           in: path
@@ -399,6 +404,7 @@
(...)