Convert to folder references where possible (#1499)

* Convert to Folder for groups that are safely already 1:1 with filesystem directories.

* Remove Mastodon/Scene/Share/View/Content/MediaView+Configuration.swift, replaced by MastodonSDK/Sources/MastodonUI, convert to folder

* Replace symlinks in Notification directories with Folder references

* Convert Discovery to Folder reference

* Convert parts of MastodonIntent to Folder references

* Convert Scene to Folder references

* Convert Documentation to Folder references

Author: aokj4ck