Reworked old events, added deprecation warnings, and improved _send

- Added a new system to show an error if old events are used
- Removed `test_data.json`, since I don't want to risk that anyone
accidentally commits their username & password
- Finished work on `sendEmoji`
- Split `_send` into two parts:
`_getSendData` and `_doSendRequest`, which allows for an easier way of
adding new send requests

test_data.json

@@ -1,6 +0,0 @@
-{
-  "email": "",
-  "password": "",
-  "user_thread_id": "",
-  "group_thread_id": ""
-}