feat: Individual page export in Markdown and HTML formats (#80)

* fix maths node

* render default html width

* Add page export module
* with support for html and markdown exports

* Page export UI
* Add PDF print too

* remove unused import

apps/client/src/features/editor/styles/placeholder.css

@@ -4,6 +4,10 @@
   color: #adb5bd;
   pointer-events: none;
   height: 0;
+
+  @media print {
+    display: none;
+  }
 }
 
 .ProseMirror .is-empty::before {
@@ -12,9 +16,17 @@
   color: #adb5bd;
   pointer-events: none;
   height: 0;
+
+  @media print {
+    display: none;
+  }
 }
 
 .ProseMirror table .is-editor-empty:first-child::before,
 .ProseMirror table .is-empty::before {
   content: '';
+
+  @media print {
+    display: none;
+  }
 }