Ftw.participation

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- Encode Mailheaders correctly.
[tschanzt]

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- Make participants view available for normal users.
The view removes the management UI (invite / remove participants) when
the user has not enough privileges.
The link to the participants view is still protected, a link can be placed
on integration level when needed.
[jone]

- Add French and English translations.
[jone]

- Update German translations.
[jone]

- Add dexterity support.
[jone]

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- Owners cannot be removed with the participants view.
[mathias.leimgruber]

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- Fix unicode decode error on participants view.
[jone]

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- Participants view: show the invitors fullname instead of his id.
[jone]

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- Add possibility to remove pending invitations on participants view.
[mathias.leimgruber]

- Fix UnicodeDecodeError in participants listing.
[mathias.leimgruber]

- Set roles field on invitation form to required if multiple roles is disabled.
[mathias.leimgruber]

- Allow granting "Reader" role when single roles is configured.
[jone]

- Possibility to configure if only one or multiple roles can be passed
on invite form.
[mathias.leimgruber]

- Remove unnecessary informations on participants view,
add better description
[mathias.leimgruber]

- Open invite form in a overlay.
[mathias.leimgruber]

- Show all participants and pending invitations on participants
overview.
[mathias.leimgruber]