Add user settings page

[kgilles]

Note: This doesn't include the full settings page. For now it's only the basic settings. Password changes and blocks will be added in a future PR.

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Creating a new page for hosting and managing user settings for authenticated users.

With this comes some bonuses such as allowing initial values on some input components, feed type and sort selector using the user's settings, a toast library, and more thorough revalidation.

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[lazyguru]

Lgtm