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

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()

layout/includes/header/post-info.pug

@@ -1,3 +1,4 @@
+- let comments = theme.comments
 #post-info
   h1.post-title= page.title || _p('no_title')
     if theme.post_edit.enable
@@ -51,15 +52,28 @@
             span.post-meta-label= _p('post.min2read') + ':'
             span= min2read(page.content, {cn: 350, en: 160}) + _p('post.min2read_unit')
     
-      if theme.busuanzi.page_pv
+      //- for pv and count
+      mixin pvBlock(parent_id,parent_class)
         span.post-meta-separator |
-        span.post-meta-pv-cv
+        span(class=parent_class id=parent_id)
           i.far.fa-eye.fa-fw.post-meta-icon
           span.post-meta-label=_p('post.page_pv') + ':'
-          span#busuanzi_value_page_pv
+          if block
+            block
 
-      if !theme.comments.lazyload && page.comments !== false && theme.comments.use && theme.comments.count
-        - var whichCount = theme.comments.use[0]
+      if theme.busuanzi.page_pv
+        +pvBlock('','post-meta-pv-cv')
+          span#busuanzi_value_page_pv
+      else if comments.use && !comments.lazyload
+        if (comments.use.includes('Valine') && theme.valine.visitor) || (comments.use.includes('Waline') && theme.waline.visitor)
+          +pvBlock(url_for(page.path),'leancloud_visitors')
+            span.leancloud-visitors-count
+        else if (comments.use.includes('Twikoo') && theme.twikoo.visitor)
+          +pvBlock('','')
+            span#twikoo_visitors
+
+      if comments.count && !comments.lazyload && page.comments !== false && comments.use
+        - var whichCount = comments.use[0]
 
         mixin countBlock
           span.post-meta-separator |