[Enhancement] Select widget_color while creating inbox (#362)

* [Enhancement] Select widget_color while creating inbox

* Fix codeclimate issues

* Fix !important

app/views/api/v1/inboxes/index.json.jbuilder

@@ -10,6 +10,7 @@ json.data do
       json.channel_type inbox.channel_type
       json.avatar_url inbox.channel.try(:avatar).try(:url)
       json.page_id inbox.channel.try(:page_id)
+      json.widget_color inbox.channel.try(:widget_color)
       json.website_token inbox.channel.try(:website_token)
     end
   end