Shortcodes for YouTube and iframes

Added shortcodes 2.5.0 as dependency; Earlier versions corrupted
non-ASCII characters, see
https://github.com/dmulholland/shortcodes/issues/6

The rendered elements have a `shortcode` CSS class.

The YouTube shortcode supports various ways to refer to a video:

    - `{youtube VideoID}`
    - `{youtube youtube.com or youtu.be URL}`

URLs containing an '=' should be quoted, or otherwise the shortcodes
library will parse it as "key=value" pair.

The IFrame shortcode supports the `cap` and `nocap` attributes. `cap`
indicates the required capability the user should have in order to
render the tag. If `nocap` is given, its contents are shown as a message
to users who do not have this tag; without it, the iframe is silently
hidden.

`{iframe src='https://source' cap='subscriber' nocap='Subscribe to view'}`

Merged test code + added HTML class for shortcode iframes

tests/test_api/test_markdown.py

@@ -1,12 +1,9 @@
-import copy
-
 from pillar.tests import AbstractPillarTest
 from pillar.tests import common_test_data as ctd
 
 
 class CoerceMarkdownTest(AbstractPillarTest):
     def test_node_description(self):
-        from pillar.markdown import markdown
         pid, uid = self.create_project_with_admin(24 * 'a')
         self.create_valid_auth_token(uid, 'token-a')
         node = {
@@ -23,10 +20,10 @@ class CoerceMarkdownTest(AbstractPillarTest):
         node_id = created_data['_id']
 
         json_node = self.get(f'/api/nodes/{node_id}', auth_token='token-a').json()
-        self.assertEqual(markdown(node['description']), json_node['_description_html'])
+        self.assertEqual('<h1>Title</h1>\n<p>This is content.</p>\n',
+                         json_node['_description_html'])
 
     def test_project_description(self):
-        from pillar.markdown import markdown
         from pillar.api.utils import remove_private_keys
 
         uid = self.create_user(24 * 'a', token='token-a')
@@ -50,4 +47,25 @@ class CoerceMarkdownTest(AbstractPillarTest):
         json_proj.pop('node_types', None)  # just to make it easier to print
         import pprint
         pprint.pprint(json_proj)
-        self.assertEqual(markdown(proj['description']), json_proj['_description_html'])
+        self.assertEqual('<h1>Title</h1>\n<p>This is content.</p>\n',
+                         json_proj['_description_html'])
+
+    def test_comment_shortcodes(self):
+        pid, uid = self.create_project_with_admin(24 * 'a')
+        self.create_valid_auth_token(uid, 'token-a')
+        node = {
+            'node_type': 'group',
+            'name': 'Test group',
+            'description': '# Title\n\n{test a="b"}',
+            'properties': {},
+            'project': pid,
+            'user': uid,
+        }
+
+        created_data = self.post('/api/nodes', json=node, expected_status=201,
+                                 auth_token='token-a').json()
+        node_id = created_data['_id']
+
+        json_node = self.get(f'/api/nodes/{node_id}', auth_token='token-a').json()
+        expect = '<h1>Title</h1>\n<!-- {test a="b"} -->\n'
+        self.assertEqual(expect, json_node['_description_html'])