Request to add 7TV, another third party emote service

[yanghuaxuan]

Add support for 7tv, another third party emote service like BTTV or FFZ.

[goldbattle]

Information:

• website: https://7tv.app/
• github org: https://github.com/SevenTV
• github golang server: https://github.com/SevenTV/ServerGo/

GraphQL Endpoint:

• api schema: https://github.com/SevenTV/ServerGo/blob/master/src/server/api/v2/gql/scheme/scheme.gql
• graphql endpoint: https://api.7tv.app/v2/gql
• use this explorer: https://graphiql-online.com/

Rest API:

• https://github.com/SevenTV/ServerGo/blob/master/docs/rest-api.md
• https://api.7tv.app/v2/emotes/global

Didn't investigate that far to be honest.