Fix identity creation & clean it up:
- Fix CreateIdentityPage to be self-contained by adding the missing nickname input. This fixes identity creation not working from the LogInPage
- Don't inline identity creation controls on OwnIdentitiesPage, only link to CreateIdentityPage
- Move all code & l10n for generating the identity creation UI to CreateIdentityPage
- This fixes bug https://bugs.freenetproject.org/view.php?id=6068