Offline accounts

[ghost]

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We currently only have online account options implemented, however "offline accounts" could be the solution in my opinion for someone that wants to use the app almost to it's full extent while not relying on Reddit and would like to preserve it's privacy. There could be multiple accounts with different names and colors. There are already subreddits added by default which is a great starter.

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When clicking on the account icon at the top (or even getting a binary option prompt at the very first start of the app) we should get a separate option for an "Offline account". It would save everything locally like saved posts, comments, subscribed subreddits, local multireddits or "Groups", and potentially Filters (#478). We could export these profiles or accounts locally into a file. There could be an option to import and export settings separately or together with the account. I made an issue for that as well that details this further: [#476].

#229 and #249 is related.

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