Added support for ```mermaid (#729)

* Added support for ```mermaid
* Fixed issue when no shortcode mermaid is present
* Change block render to match shortcode
* Remove mermaid logic from base

---------

Co-authored-by: CharlesPhilippeLabbe <c.p@o-possum.com>
Co-authored-by: Alex Shpak <alex-shpak@users.noreply.github.com>

layouts/_default/_markup/render-codeblock-mermaid.html

@@ -0,0 +1,12 @@
+{{ if not (.Page.Store.Get "mermaid") }}
+<!-- Include mermaid only first time -->
+<script src="{{ "mermaid.min.js" | relURL }}"></script>
+{{ with resources.Get "mermaid.json" }}
+  <script>mermaid.initialize({{ .Content | safeJS }})</script>
+{{ end }}
+{{ .Page.Store.Set "mermaid" true }}
+{{ end }}
+
+<pre class="mermaid">
+  {{- .Inner -}}
+</pre>