Offer bypass for instance slur filter affecting external comments

[Sjmarf]

A user might write a comment on an instance where a certain word is not censored. When that comment gets federated to an instance where that word is censored, it gets replaced with *removed*. It's not exactly clear in the UI why a user might be seeing *removed* everywhere. We should add a footer to affected comments explaining this, and offer to fetch the comment from the host instance instead to bypass the filter. We should also have an opt-in setting to always do this, without asking the user first.