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

layout/includes/head/Open_Graph.pug

@@ -1,6 +1,6 @@
 if theme.Open_Graph_meta
   - let contentType = is_post() ? 'article' : 'website'
-  - let metaImage = full_url_for(page.cover || theme.avatar.img)
+  - let metaImage = (page.cover || theme.avatar.img) ? full_url_for(page.cover || theme.avatar.img) : ''
   - let fb_appId = theme.facebook_comments.app_id || ''
   - let fb_admins = theme.facebook_comments.user_id || ''
 

layout/includes/header/index.pug

@@ -1,6 +1,6 @@
 if !theme.disable_top_img && page.top_img !== false
   if is_post()
-    - var top_img = page.top_img || page.cover || page.randomcover || theme.default_top_img
+    - var top_img = page.top_img || page.cover || page.randomcover
   else if is_page()
     - var top_img = page.top_img || theme.default_top_img
   else if is_tag()