Made further tweaks to align with current editor

- Ensured each of the core actions worked at a high level.
- Handled some TinyMCE API changes.
- Moved code block insert to its own button.

resources/sass/_tinymce.scss

@@ -19,6 +19,10 @@
   line-height: 1.6;
 }
 
+.page-content.mce-content-body > :last-child {
+  margin-bottom: 5rem;
+}
+
 .tox-toolbar__primary {
   justify-content: center;
 }