feat: 添加waline,valine 和twikoo 提供的文章閲讀數配置 close #502

improvement: 當文章頁cover 和cover 的 default_img都沒有配置時，會去讀取default_top_img的參數
improvement: 在完全沒有配置的情況下，運行時控制臺報null 的問題

_config.yml

@@ -321,6 +321,7 @@ valine:
   emojiCDN: # emoji CDN
   enableQQ: false # enable the Nickname box to automatically get QQ Nickname and QQ Avatar
   requiredFields: nick,mail # required fields (nick/mail)
+  visitor: false
   option:
 
 # waline - A simple comment system with backend support fork from Valine
@@ -330,6 +331,7 @@ waline:
   avatar: monsterid # gravatar style https://zh-tw.gravatar.com/site/implement/images/#default-image
   emojiCDN: # emoji CDN
   bg: # waline background
+  visitor: false
   option:
 
 # utterances
@@ -356,6 +358,7 @@ facebook_comments:
 twikoo:
   envId:
   region:
+  visitor: false
   option:
 
 # Chat Services