Allow clients to preserve full channel histories locally

The ability to download media has an entirely different use case. Fluxer's main instance necessarily deletes attached media after a certain amount of time, which destroys the context of past conversations. Not all users will mind this, but there are many long-term friend groups and small communities that highly value past conversations and refer back to them regularly. Just downloading the media doesn't place the media in-line, where it was at the time. I do not anticipate the average user needing this, so I'd expect the settings to be disabled by default, and enabled by power users, archivists, server admins, important community contributors, anyone who wants to preserve material long-term. The point is to let us, the users, keep Fluxer's chatlogs in place with media included, without taxing Fluxer (the company) itself.