Add hashtag filter to profiles

[Gargron]

Allow browsing a profile by a specific hashtag. Useful for artists.

Public profile change: GET /@:username/tagged/:hashtag
REST API change: GET /api/v1/accounts/:id/statuses?tagged=:hashtag

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TODO:

• Public profile page route
• REST API
• List of browserable hashtags in sidebar on public profile

[MirceaKitsune]

Will this also work for the search bar? For instance you could use #sometag@username@domain to only list posts containing that tag from the user in cause. Additionally just #sometag@domain would be a very welcome syntax, allowing you to search for a tag on a specific instance only.

[krainboltgreene]

Not sure what the project's preference is, but I've been seeing a lot of people move from #[] to #fetch() since it tells the reader a lot more about the intent. For example, in this method we EXPECT :tag to be a key, thus params.fetch(:tag), but if we didn't params.fetch(:tag, nil) and of course we get all the niceness of #fetch's other default api: fetch(:key) {dynamicvalue}.

Either way, seems like what you want here could also be expressed as: Status.tagged_with(Tag.where(name: params[:tag]).pluck(:id).first), though if tagged_with allows an array you can just drop .first.