Additional fields and features for Mastodon

[cdp1337]

I added a few additions to my fork of the code. Interested in merging them upstream?

https://github.com/zorn-v/nextcloud-social-login/compare/master...cdp1337:nextcloud-social-login:master

Notably:

• Usernames are imported from Mastodon
• Profile images are imported from Mastodon
• Groups are imported from Roles in Mastodon
• Fediverse URL is imported from Mastodon
• Description/Bio is imported from Mastodon
• The identifier update changes the username from "Mastodon-123456789123" to the actual Mastodon username.

The last one should be configurable if you're interested in them, as having that along with other providers / local users would be problematic for admins.

[zorn-v]

What happen if "there is account exists" ? Just imagine it is admin account )