SqlServerOptimisticConcurrencyTests fail if run without an existing data...

...base, being unable to insert values in the Id columns, when seeding the database, because they are marked with IDENTITY.

The fix adds an IsIndentity extension to property extensions and updates the related code to use it. The implementation of the getter needs to be revisited to determine whether the condition "strategy == null && Property.PropertyType.IsInteger()" is truly needed or not. Without it a bunch of tests fail currently because the Id columns are not marked as IDENTITY.

Also, I updated SqlServerF1Fixture.OnModelCreating to UseSequence for the Id columns that the test inserts values into, in order to unblock the clean test runs. This may need to be revisited, based on what is decided about the IDENTITY behavior mentioned above.