Add support for full accountless Anonymous experience

The current implementation of Anonymous mode is a bit too barebones and could be improved significantly

• Subscriptions

Currently we have a list of default subscriptions which we cannot change to my best knowledge. If we were provided a default list, add support for exporting to or importing from subscriptions from a .json or with other import methods, like from other multireddits. Allow bulk management, selecting and deleting subreddits, so with a fresh new install we could quickly wipe the subsciption list and import our own or perhaps we could even immediately replace the list or the whole database.

• Saving content

Add support for saving posts and comments locally.

• Database import/export

Using a local database we could make things more straightforward and private. We should export and import this database including the saved content, subscriptions, settings, everything.

No files or tests are named. Start by locating the Anonymous mode, subscription handling, saved-content handling, and local database code, then determine how these areas currently persist data. Done would require a coherent design and implementation for subscription import/export and bulk management, local post and comment saving, and complete database import/export.