Django-clickclack

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* add new property "is_active" to schedule model
* add deprecation warning for properties "must_be_turned_off" and "must_be_turned_on"

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* use parsed valid_from in admin changelist

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* updated localization files
* always show current year in date

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* fixed lookup (last release is broken)

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* fixed lookup for period-manager

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* add "Save as" button to period admin