Fix issue of [ENSession noteStoreForNotebook:] not returning proper store for linked notebook

If input notebook is a shared notebook, the returned note store will not work properly because the note store client delegate is not set.

To solve this issue simply call [ENSession noteStoreForLinkedNotebook:] which will setup delegate properly.
Merge pull request #23 from siuying/notestore-shared

Fix issue of [ENSession noteStoreForNotebook:] not returning proper store for linked notebook