add template folder CRUD

* create template folder
* rename template folder
* get list of template folders for service (not nested/presented in any
  particular way)
* delete template folder

Also removed `lazy=dynamic` from the `template_folder.templates`
relationship. lazy=dynamic returns a query object (which you can then
filter further). We just want to return the entire fetched list, at
least for now.

tests/app/db.py

@@ -48,7 +48,8 @@ from app.models import (
     FactBilling,
     FactNotificationStatus,
     Complaint,
-    InvitedUser
+    InvitedUser,
+    TemplateFolder,
 )
 
 
@@ -690,3 +691,10 @@ def create_invited_user(service=None,
     invited_user = InvitedUser(**data)
     save_invited_user(invited_user)
     return invited_user
+
+
+def create_template_folder(service, name='foo', parent=None):
+    tf = TemplateFolder(name=name, service=service, parent=parent)
+    db.session.add(tf)
+    db.session.commit()
+    return tf