Move configuration from config.py to config.json and add support for GitHub organization webhooks

remove _format_watch() from utils.github_webhook as the value of
watchers_count is always identical with stargazers_count
https://docs.github.com/en/developers/webhooks-and-events/webhook-events-and-payloads#watch
https://developer.github.com/changes/2012-09-05-watcher-api/

config.py

@@ -0,0 +1,12 @@
+import json
+from os import environ
+
+if environ.get('DYNO'):
+    data = json.loads(environ.get("HOOK_CONFIG"))
+else:
+    with open("config.json") as f:
+        data = json.load(f)
+
+BOT_TOKEN = data['bot_token']
+PORT = data.get('port')
+GH_WEBHOOKS = data['gh_webhooks']