Change group/circle "Settings" UI to be more like the "Settings" tab

All of the old "settings" interfaces are still using modal SwiftUI sheet dialogs, because that's all that really worked in the early days of SwiftUI. But now we have NavigationStack and we can easily created stacked navigation interfaces that look nicer.

For a group:

• Move "Configure Group", "Manage Members", and "Security" from the main menu into a new "Settings" screen
• Settings screen should have
  • Cover photo
  • Group name
  • Topic
  • Manage members
  • Security

For a circle:

• Move "Connections" and "Settings -> New Cover Photo" from the main menu into a new "Settings" screen
• Settings screen should have
  • Cover photo
  • People I'm following
  • My followers