Adopting a challenge type layout from deckar01 (#399)

* Adopting a challenge type layout from deckar01
* Move standard challenge modals into the plugin
* Migration to change challenge type id to a string
* Travis testing now builds with MySQL, SQLite, and Postgres
* Rework get_standings to use the row ID instead of the saved time because of differences in database time precision

tests/user/test_challenges.py

@@ -268,3 +268,4 @@ def test_that_view_challenges_unregistered_works():
         data = r.get_data(as_text=True)
         data = json.loads(data)
         assert data['status'] == -1
+    destroy_ctfd(app)