Need to add IsolatedStorageFile Get*StoreFor*() static factory methods.

This includes:

GetUserStoreForDomain()
GetUserStoreForAssembly()
GetUserStoreForApplication() <- Need to update implementation
GetUserStoreForSite()
GetMachineStoreForDomain()
GetMachineStoreForAssembly()
GetMachineStoreForApplication()

Other factory methods will be broken out into separate work items as there are more direct dependencies on System.Security.Policy.Evidence.