Fixed compilation errors for portable class library
Fixed imports from core solution

Fixed import of string resources and tidied up import of EntityFramework
code.
Excluded test that won't work under PCL test framework

Conditionally excludes a test that relies on the server being run at a
particular location.
Allow PCL to use REST client.
Ignore tests that are not working due to dotNetRDF limitations
Fixed tests to make them repeatable
Fixed ListSubDirectories implementation
Fixed tests to make them repeatable