Extended account lookup API

[Tunous]

• Changed lookup function to return Account as documented by Mastodon: https://docs.joinmastodon.org/methods/accounts/#lookup
• Added pleroma and akkoma support by internally using id based endpoint as these support URI: https://docs-develop.pleroma.social/backend/development/API/differences_in_mastoapi_responses/#accounts
• Pixelfed remains unsupported
• Friendica remains unsupported: https://wiki.friendi.ca/docs/api-mastodon#currently_unimplemented_endpoints
• Additionally changed domain blocking in Relationship as it is returned as nil for pixelfed

[kkostov]

Nicely done! I love the refactor for requireFlavour!