Add option to automatically expand content warnings

I personally don't need content warnings so in the official (not really official I guess) client I check the option to automatically expand all content warnings. It would be great to have this option in phanpy.

Start by locating Phanpy's content-warning rendering and the existing settings or options UI. Add a user-controllable option for automatically expanding content warnings, and verify that content warnings expand when the option is enabled while retaining the current behavior when it is disabled.

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