Add Parse post-save callback to remedy missing objectID issue

This commit adds a post-save callback to Parse objects after they have
been inserted. This remedies a situation where multiple new objetcs
cannot be related to eachother.
Merge branch 'master' of https://github.com/sbonami/PFIncrementalStore into 21-Multiple-inserted-object-relationships-do-not-save

* 'master' of https://github.com/sbonami/PFIncrementalStore:
  Modify Travis test procedures
  Fix Rakefile so Travis test failures are properly reported
  Fix tests for changes in 2efb10f
  Add missing relationship implementation to InsertOrUpdate method
Modify spec tests for updated Parse sync method

This commit modifies the stubs for `setValuesFromManagedObject:` by
appending the callback argument to the selector.
Merge pull request #21 from sbonami/21-Multiple-inserted-object-relationships-do-not-save

Multiple inserted object relationships do not save