* Amended GetAll() on IDataTypeService to return an empty collection rather than null.
* Added a ClearSessionValue method to ISessionManager (given you can no longer set a value to null).
* Allow for null values in a StatefulNotification.
* Removed obsoletion of synchronous messages on TreeControllerBase.
* Fixed further CS8620 warnings in core project.
* Further fix to nullable warning.
* Aligned nullablility of retreiving tree nodes and menus, synchronously or asynchronously (such that we no longer can get null values, always empty collection objects).
* Rename Umbraco.Core namespace to Umbraco.Cms.Core
* Move extension methods in core project to Umbraco.Extensions
* Move extension methods in core project to Umbraco.Extensions
* Rename Umbraco.Examine namespace to Umbraco.Cms.Examine
* Move examine extensions to Umbraco.Extensions namespace
* Reflect changed namespaces in Builder and fix unit tests
* Adjust namespace in Umbraco.ModelsBuilder.Embedded
* Adjust namespace in Umbraco.Persistence.SqlCe
* Adjust namespace in Umbraco.PublishedCache.NuCache
* Align namespaces in Umbraco.Web.BackOffice
* Align namespaces in Umbraco.Web.Common
* Ensure that SqlCeSupport is still enabled after changing the namespace
* Align namespaces in Umbraco.Web.Website
* Align namespaces in Umbraco.Web.UI.NetCore
* Align namespaces in Umbraco.Tests.Common
* Align namespaces in Umbraco.Tests.UnitTests
* Align namespaces in Umbraco.Tests.Integration
* Fix errors caused by changed namespaces
* Fix integration tests
* Undo the Umbraco.Examine.Lucene namespace change
This breaks integration tests on linux, since the namespace wont exists there because it's only used on windows.
* Fix merge
* Fix Merge
