Again at @li's request, images in a CW are now collapsed behind the CW! They are also no longer turned off by default -- the thought is that if you're opening the CW you probably want to see the whole message, and why bother with 2 clicks when it can be one? Anyway here is a gif of it in action.
As always, let me know if this behavior doesn't work for you in some way and I'll revert it.
Link to git commit: https://github.com/friendcamp/mastodon/commit/75d00a4ea1f9151ddfd1e0aeed07901f9f07862d
