#14 [WIP] Blacklist command

Implement a blacklist with command that we want to prevent being run from occweb like ```maintenance mode:on``` Return a 403 forbidden with a json response ``` { "error": "command blacklisted"} ``` The error message is formatted for term but nextcloud is escaping color code \u001b -> \\u001b in the response Will see to move the formatting of the error in the js

The [blacklisted command](https://git.adphi.net/adphi/occweb/pulls/14/files#diff-c62a13695dd9007bbfeca860cb9f55cf0ab59beR30) is not correct (see [occ docs](https://docs.nextcloud.com/server/18/admin_manual/configuration_server/occ_command.html#maintenance-commands)): `maintenance:mode --on`. I would change the [error message](https://git.adphi.net/adphi/occweb/pulls/14/files#diff-c62a13695dd9007bbfeca860cb9f55cf0ab59beR75) to something more meaningful as "command not supported in occweb" with maybe a link to the docs. In some cases, I think it can be useful in the future to be able to bypass the blacklist with `--force` and `-f` or a custom flag if not available.