Ftw.participation

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- Fix unicode errors in activity renderer. [jone]

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- Add ftw.activity support for participation events. [jone]

- Add events. [jone]

- Drop Plone 4.1 and 4.2 support. [jone]

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- Change german translation for the InvitationAccepted text.
[raphael-s]

- Check if we actually have a invitation for an id in the session.
[tschanzt]

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- Fix condition for invite_participants view.
Only raise NotFound if both options (invite email/member) are disabled.
[mathias.leimgruber]

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- BugFix: Pass email_from as string, not as email.header instance.
This fixes sending emails with an Exchange.
[mathias.leimgruber]

- Do not show invite link, if internal user and email invitation is disabled.
[mathias.leimgruber]

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- Update Translations.