Split RLMArray into RLMArray + RLMResults

Splits RLMArray into separate apis.

The relevant apis should now be updated along with inline docs. All osx tests currently pass. We will still need to update the rest of the docs on the website separately.
I still think that treating a missing table as an empty table is both the friendlier thing to do and more consistent with read-write realms, since we don't force a migration when a table is added.