There was a bug with changing timestamps using the topic wrench button. Under some circumstances, a topic was disappearing from the top of the latest tab after changing timestamps. Steps to reproduce:
- Choose a topic on the latest tab (the topic should be created some time ago, but has recent posts)
- Change topic timestamps (for example, move them one day forward):
- Go back to the latest tab and see that topic has disappeared.
This PR fixes this. We were setting topic.bumped_at to the timestamp user specified on the modal. This is incorrect. Instead, we should be setting topic.bumped_at to the created_at timestamp of the last regular (not a whisper and so on) post on the topic.
This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
