Ftw-usermanagement

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- Add tests for the whole package.
[eschmutz]

- Full refactored and improved performance if we have many
users and groups.
[eschmutz]

- Remove ability to sort on title of users or groups.
[eschmutz]

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- Fix sending userinfos and/or password
[mathias.leimgruber]

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- Added group id validator.
[mathias.leimgruber]

- Fix display name in group_membership.
[mathias.leimgruber]

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- Added i18n domain.
[mathias.leimgruber]

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- Use token of principal user source (This supports diffrent plone configs).
[mathias.leimgruber]

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- Removed custom viewletmanager, it's no longer necessary.
[mathias.leimgruber]