Tidy up validate-modules ignores for notification modules (#1229)

* fixed validation-modules for plugins/modules/notification/bearychat.py

* fixed validation-modules for plugins/modules/notification/campfire.py

* fixed validation-modules for plugins/modules/notification/catapult.py

* fixed validation-modules for plugins/modules/notification/flowdock.py

* fixed validation-modules for plugins/modules/notification/grove.py

* fixed validation-modules for plugins/modules/notification/hipchat.py

* fixed validation-modules for plugins/modules/notification/irc.py

* fixed validation-modules for plugins/modules/notification/jabber.py

* fixed validation-modules for plugins/modules/notification/logentries_msg.py

* fixed validation-modules for plugins/modules/notification/mail.py

* fixed validation-modules for plugins/modules/notification/matrix.py

* fixed validation-modules for plugins/modules/notification/mattermost.py

* fixed validation-modules for plugins/modules/notification/mqtt.py

* fixed validation-modules for plugins/modules/notification/nexmo.py

* fixed validation-modules for plugins/modules/notification/office_365_connector_card.py

* fixed some docs issues in plugins/modules/notification/pushbullet.py, but cannot remove the ignore lines yet

* fixed validation-modules for plugins/modules/notification/pushover.py

* fixed some docs issues in plugins/modules/notification/rocketchat.py, but cannot remove all ignore lines yet

* fixed validation-modules for plugins/modules/notification/say.py

* fixed validation-modules for plugins/modules/notification/sendgrid.py

* fixed validation-modules for plugins/modules/notification/slack.py

* fixed validation-modules for plugins/modules/notification/syslogger.py

* fixed validation-modules for plugins/modules/notification/telegram.py

* fixed validation-modules for plugins/modules/notification/twilio.py

* fixed validation-modules for plugins/modules/notification/typetalk.py

* Enabling validation-modules for modules in: notification

* removed naughty trailing space

plugins/modules/notification/mattermost.py

@@ -22,10 +22,12 @@ description:
 author: "Benjamin Jolivot (@bjolivot)"
 options:
   url:
+    type: str
     description:
       - Mattermost url (i.e. http://mattermost.yourcompany.com).
     required: true
   api_key:
+    type: str
     description:
       - Mattermost webhook api key. Log into your mattermost site, go to
         Menu -> Integration -> Incoming Webhook -> Add Incoming Webhook.
@@ -33,17 +35,21 @@ options:
         http://mattermost.example.com/hooks/C(API_KEY)
     required: true
   text:
+    type: str
     description:
       - Text to send. Note that the module does not handle escaping characters.
     required: true
   channel:
+    type: str
     description:
       - Channel to send the message to. If absent, the message goes to the channel selected for the I(api_key).
   username:
+    type: str
     description:
       - This is the sender of the message (Username Override need to be enabled by mattermost admin, see mattermost doc.
     default: Ansible
   icon_url:
+    type: str
     description:
       - Url for the message sender's icon.
     default: https://www.ansible.com/favicon.ico