Collective.dms.scanbehavior

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- Nothing changed yet.

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- Corrected behavior zcml definition to avoid message when Plone starts.
[sgeulette]

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- Improved date range.
[sgeulette]
- Cleanup: isort, use `unittest` instead `unittest2`,
removed dependency on `ecreall.helpers.testing`.
[gbastien]

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- fix : [DMS-949] min & max for scan_date
[bleybaert]

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- Added field `to_sign` to the behavior.
[gbastien]

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- Moved version attribute to the scan tab.
[gbastien]
- Move the signed attribute from IDmsFile schema
[mpeeters]
- Added signed index
[sgeulette]