Server settings UI

[dario-piotrowicz]

~Draft waiting for #339 to get merged first~ ~We also need to first implement an admin flag before this can be merged~

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TODO

• [x] Update code based on ADMIN_EMAIL and new is_admin flag
• [x] Set the first account as admin (both as a migration and when the first account is added to the actors table)
• [x] Fix the rules endpoint to follow the mastodon API
• [x] Remove random numbers
• [ ] squash fixup commits before merging

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Pages Implemented: