Commit after every full record insertion/update (closes #135)

Docs say that TransactionTooLargeException is thrown when the buffer reaches 1 MB. Because we can't know
how large a single insertion/update is and there may be contacts with larger photos, it's only safe to
commit after every insertion/update. If photos exceed ~ 900 kB it would be required to write the photos
to an asset file (maybe I'll do this later, then we can group insertions/updates again).