Add "reject quotes" settings

What does this MR do?

Adds settings to "reject quotes" from a user or instance. If applied to a local user, then they will be unable to make any quote posts. The UI controls are disabled and the API returns an error. If applied to a remote user or instance, then the quote will be stripped and a "processing error" will be recorded for the note. This displays an additional warning banner indicating that the post may be missing context.

Additionally, the quote resolution code is cleaned up and improved to avoid duplicate fetches. A new "processing error" concept is implemented, allowing any federation errors / incompatibilities to be communicated to the user instead of silently ignored.

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