[ListHelper] add Enforce unique values feature
[EnsureUniqueValue] add extra security
Merge branch 'develop' of https://github.com/GSoft-SharePoint/Dynamite into develop
Merge branch 'develop' of https://github.com/GSoft-SharePoint/Dynamite into develop

Conflicts:
	Source/GSoft.Dynamite/Lists/ListHelper.cs
[StyleCop] Passed some forgotten style cop.