Fix issue with FluentMap.NullValue

Actually there were two bugs:
1) Incorrect value passed to member.Attributes.Add
2) Incorrect isSet detection in ExtensionMetadataProvider
Updated Oracle.ManagedDataAccess nuget.
Merge branch 'master' into pr/n265_kekekeks
Fixed #255. [Bug] Problem with struct when using PropertyChanged attribute.

Addressed issue with "common language runtime detected an invalid program" for nullable types.
Revert "Fixed #255. [Bug] Problem with struct when using PropertyChanged attribute."
Fixed #255. [Bug] Problem with struct when using PropertyChanged attribute.

Addressed issue with "common language runtime detected an invalid program" for nullable types.
Fixed Pliralization template.
Revert "Fixed Pliralization template."

This reverts commit 4b41ade29c070a2affa0d1b46185726c295f6118.
Fixed 268.
Merge branch 'master' of https://github.com/igor-tkachev/bltoolkit

Conflicts:
	Source/Data/DataProvider/OdpDataProvider.cs

Removed local unit tests