Nsfw tab in content settings

We have the NSFW tab in the content settings modal design, but I think the functionality is not yet ready for this to be implemented - both in backend and also in how it should work in the front end.

We do have a similar element that already exists (you can find it if you search for something, then click the settings cog on the search results page), and Mark suggested I pull that out and reuse it so something will be there in the meantime (and we can easily switch it on when it's ready), but I don't think that is worth it at this time because its current state is so far from being useful that a lot of time will have to be spent re-working it to get to a state in which the result of a selection is intuitive for the average user. (it currently works on search results only, and settings do not persist between sessions)

Things to be ironed out:

• This isn't close to being ready in the backend. My guess is that the nsfw preference is supposed to be implemented in the newsfeed, discovery trends, and search results (and channel pages?)? But we don't have anything like that at the moment. We also don't have a plan for how it should be implemented - e.g. should it be referenced primarily within the backend, or should it be passed as a query parameter in every relevant api request?

• It's unclear how this works alongside the NSFW setting in the user settings module (/settings/account/nsfw-content). How are the two related? Why are they in different places? Why does one have a second layer of checkboxes appear when the other doesn't? I think they should be in a single place, and should apply to all content.

• Side note: shouldn't the Boost settings also be in the content settings modal?