Support array for json_data posted in rest/json service (#99)

Previous syntax :
```
CURLOPT_POSTFIELDS => array(
	'auth_user' => 'admin',
	'auth_pwd' => 'admin',
	'json_data' => '{
	   "operation": "core/get",
	   "class": "Person",
	   "key": "SELECT Person", "limit": "10", "page": "1"
	}'
);
```

Now we can also use :
```
CURLOPT_POSTFIELDS => array(
	'auth_user' => 'admin',
	'auth_pwd' => 'admin',
	"json_data[operation]" => "core/get",
	"json_data[class]" => "Person",
	"json_data[key]" => "SELECT Person",
	"json_data[limit]" => 10,
	"json_data[page]" => 1
);
```

webservices/rest.php

@@ -79,7 +79,7 @@ try
 	utils::UseParamFile();
         
 	$oKPI->ComputeAndReport('Data model loaded');
-        
+
 	$iRet = LoginWebPage::DoLogin(false, false, LoginWebPage::EXIT_RETURN); // Starting with iTop 2.2.0 portal users are no longer allowed to access the REST/JSON API
         $oKPI->ComputeAndReport('User login');
         
@@ -130,11 +130,26 @@ try
 	{
 		throw new Exception("Missing parameter 'json_data'", RestResult::MISSING_JSON);
 	}
-	$aJsonData = @json_decode($sJsonString);
-	if ($aJsonData == null)
+
+	if (is_string($sJsonString))
 	{
-		throw new Exception("Parameter json_data is not a valid JSON structure", RestResult::INVALID_JSON);
-	}
+        $aJsonData = @json_decode($sJsonString);
+    }
+	elseif(is_array($sJsonString))
+    {
+        $aJsonData = (object) $sJsonString;
+        $sJsonString = json_encode($aJsonData);
+    }
+	else
+    {
+        $aJsonData = null;
+    }
+
+    if ($aJsonData == null)
+    {
+        throw new Exception('Parameter json_data is not a valid JSON structure', RestResult::INVALID_JSON);
+    }
+
 	$oKPI->ComputeAndReport('Parameters validated');