Proof of concept: Generic OAuth

[RedFlames]

Still a bunch of things I'd have to clean up, but this is more like what I had in mind for supporting arbitrary OAuth2 providers

1. Generate a random string for the OAuth2 "state" parameter, prefix it with the provider key (config name, e.g. "discord") and suffix with RSA signature of the random string (just a lil hack so that the state strings don't need to be tracked anywhere......)
2. Allow OAuth2 providers configured like so:

OAuthProviders:
  discord:
    OAuthPathAuthorize: https://discord.com/oauth2/authorize
    OAuthPathToken: https://discord.com/api/oauth2/token
    OAuthScope: identify
    OAuthClientID: xxx
    OAuthClientSecret: xxx
    ServiceUserAPI: https://discord.com/api/users/@me
    ServiceUserJsonPathUid: $.id
    ServiceUserJsonPathName: $.['global_name','username']
    ServiceUserJsonPathPfp: $.avatar
    ServiceUserAvatarURL: https://cdn.discordapp.com/avatars/{0}/{1}.png?size=64
    ServiceUserAvatarDefaultURL: https://cdn.discordapp.com/embed/avatars/0.png

(YAML is absolute lunacy with how it doesn't serialize those JSONPaths as strings......)
3. Advantages: When requesting ServiceUserAPI which we don't know what exactly it returns, just try to parse it with config-provided JSONPaths 🙂
https://www.newtonsoft.com/json/help/html/QueryJsonSelectToken.htm
https://goessner.net/articles/JsonPath/

PS: Don't mind the change in client EmojiComponent...... I was lazy with my unstaged changes :) Moved that bit to #167