[Core V3] Make the bot data path configurable (#879)

* Initial commit

* Fix sentry

* Make cog manager install path work relative to the bot's dir

* Fix downloader to save data relative to the defined data folder

* Fix sentry test

* Fix downloader tests

* Change logfile location

* Add another line to codeowners

* Basic tests

* Fix versioning

* Add in FutureWarning for config file changes

* Add reference to issue

core/cli.py

@@ -102,6 +102,9 @@ def parse_cli_flags():
     parser.add_argument("--dev",
                         action="store_true",
                         help="Enables developer mode")
+    parser.add_argument("config",
+                        nargs='?',
+                        help="Path to config generated on initial setup.")
 
     args = parser.parse_args()