Ftw-usermanagement

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- Fix user_membership link.
[tschanzt]

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- Fix Usertab. It was broken when email login was active.
[tschanzt]

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- Add check if user is None in get_display_users. This prevents Group overlay from crashing.
[tschanzt]

- Show loginname instead of userid. If use_email_login isn't active the email is displayed as well.
[tschanzt]

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- fix Group Management
[tschanzt]

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- Don't remove local Roles. But remove Memberfolder.
[tschanzt]

- fix group listing in user overview.
[tschanzt]

- Handle broken user objects.
[mathias.leimgruber]

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- Add extjs compatibility
[eschmutz]