fix: add email notifications templates

templates/emails/close_issue.html

@@ -0,0 +1,4 @@
+Issue closed.
+
+--
+You can see the issue on PonyTracker: {{ uri }}

templates/emails/new_comment.html

@@ -0,0 +1,4 @@
+{{ comment }}
+
+--
+Respond on PonyTracker: {{ uri }}

templates/emails/new_issue.html

@@ -0,0 +1,8 @@
+{% if description %}
+{{ description }}
+{% else %}
+  No description.
+{% endif %}
+
+--
+Comment it on PonyTracker: {{ uri }}

templates/emails/reopen_issue.html

@@ -0,0 +1,4 @@
+Issue reopened.
+
+--
+You can see the issue on PonyTracker: {{ uri }}