Access token branch saif

FIles To Review

1..AccessTokenDataBase.cs
2..CustomException.cs
3.IAccessToken.cs
4.TokenAccessService.svc
5.AccessTokenFixture.cs

The use of a private static List might make is complicated to test this component. 
Multiple tests would mutate the same list and you might not be able to assume that the state of the list is what 
your test needs. The fact that your tests do not seem to be breaking right now is a good sign that your fixtures are not comprehensive enough since this would be pretty easy to break.