Hide\blur images when sensitive flag set to true

[jk-na]

This is a known missing feature so far as I understand (as field was missing from go-fed) so just raising the ticket as a placeholder.

When I post a sensitive\content warning status via the API with an image attached, the status is correctly collapsed behind the subject but currently the image is not hidden, even if sensitive=true.

[tsmethurst]

We've got a PR open against go-fed rn for adding the sensitive property: go-fed/activity#154

If this is accepted, we can add this into GtS as well 🤞