Allow sync of Github comments without common username and add unit tests

docs/api-json-rpc.markdown

@@ -2823,7 +2823,7 @@ Response example:
         "id": "1",
         "task_id": "1",
         "user_id": "1",
-        "date": "1410881970",
+        "date_creation": "1410881970",
         "comment": "Comment #1",
         "username": "admin",
         "name": null
@@ -2861,7 +2861,7 @@ Response example:
     "result": [
         {
             "id": "1",
-            "date": "1410882272",
+            "date_creation": "1410882272",
             "task_id": "1",
             "user_id": "1",
             "comment": "Comment #1",

docs/github-webhooks.markdown

@@ -82,7 +82,7 @@ When a task is created from a Github issue, the link to the issue is added to th
 - Choose the event: **Github issue assignee change**
 - Choose the action: **Change the assignee based on an external username**
 
-Note: The username must be the same between Github and Kanboard.
+Note: The username must be the same between Github and Kanboard and the user must be member of the project.
 
 ### Assign a category when an issue is tagged on Github
 
@@ -95,4 +95,5 @@ Note: The username must be the same between Github and Kanboard.
 - Choose the event: **Github issue comment created**
 - Choose the action: **Create a comment from an external provider**
 
-Note: The username of the comment author must be the same between Github and Kanboard and the task must exists before.
+If the username is the same between Github and Kanboard the comment author will be assigned, otherwise there is no author.
+The user also have to be member of the project in Kanboard.

docs/webhooks.markdown

@@ -198,7 +198,7 @@ Comment creation:
     "task_id": "1",
     "user_id": "1",
     "comment": "test",
-    "date": 1431991615
+    "date_creation": 1431991615
   }
 }
 ```