Implement Discord OAuth auth provider

Create the OAuth functionality, implement as a serviceprovider(?). In terms of who to allow access to, an admin role will be implemented. This will act similar to the Teamspeak's "server admin" role in which the user has full access to everything except giving the "server admin" role to anyone else (since that could be exploited).

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*Original: https://github.com/2bnb/website/projects/1#card-30534028*