Add valine comment system support (#446)

* feat: add valine support

* Adjust the comment config

* Adjust the comment config

* Make comment section backward compatible with old config

Signed-off-by: hossainemruz <hossainemruz@gmail.com>

Co-authored-by: hossainemruz <hossainemruz@gmail.com>

layouts/partials/valine.html

@@ -0,0 +1,17 @@
+<!-- valine -->
+<div id="vcomments"></div>
+<script src="//cdn1.lncld.net/static/js/3.0.4/av-min.js"></script>
+<script src="//unpkg.com/valine/dist/Valine.min.js"></script>
+<script type="text/javascript">
+  new Valine({
+    el: "#vcomments",
+    appId: "{{ .valine.appId }}",
+    appKey: "{{ .valine.appKey }}",
+    avatar: "{{ .valine.avatar }}",
+    placeholder: "{{ .valine.placeholder }}",
+    visitor: "{{ .valine.visitor }}",
+    lang: "{{ .valine.lang }}",
+    recordIP: "{{ .valine.recordIP }}",
+    enableQQ: "{{ .valine.enableQQ }}",
+  });
+</script>