Minor changes to some of the Queue and related classes

Noticed that the IsolatedStorageQueueStore used typeof(FolderQueueStore) instead of typeof(IsolatedStorageQueueStore)
ExceptionlessClient: a _nullLogger is declared and then another one created in ctor.
FolderQueueStore: Use ?? and conditionally declare files in GetManifests
InMemoryQueueStore: Conditionally declare manifests in GetManifests
ModelSerializer: Change GetSettings to private and static, changed IsIntrinsicType to static