Added new structure (input prompt and inner cell) to markdown cells.

IPython/nbconvert/templates/html/basic.tpl

@@ -55,8 +55,11 b' In [{{ cell.prompt_number }}]:'
 
 {% block markdowncell scoped %}
 <div class="text_cell_render border-box-sizing rendered_html">
+<div class="prompt input_prompt"></div>
+<div class="inner_cell">
 {{ cell.source  | markdown2html | strip_files_prefix }}
 </div>
+</div>
 {%- endblock markdowncell %}
 
 {% block headingcell scoped %}