Add markdown support

Author: jahn96

src/CodeSnippetDisplay.tsx

@@ -26,6 +26,7 @@ import {
   pythonIcon,
   fileIcon,
   rKernelIcon,
+  markdownIcon,
 } from '@jupyterlab/ui-components';
 import { CodeEditor, IEditorServices } from '@jupyterlab/codeeditor';
 import * as nbformat from '@jupyterlab/nbformat';
@@ -669,6 +670,18 @@ export class CodeSnippetDisplay extends React.Component<
           />
         );
       }
+      case 'Gfm': {
+        return (
+          <markdownIcon.react
+            tag="span"
+            height="16px"
+            width="16px"
+            right="7px"
+            top="5px"
+            margin-right="3px"
+          />
+        );
+      }
       case 'Java': {
         return (
           <javaIcon.react

src/CodeSnippetLanguages.ts

@@ -67,6 +67,7 @@ export const SUPPORTED_LANGUAGES = [
   'F#',
   'Go',
   'Galileo',
+  'Gfm',
   'Erlang',
   'PARI/GP',
   'Aldor',