Simperium Mk 0.6.7

**Release Details:**

- Issue #250: Fixes a bug that caused relationships to fail during initial dataset download.
- Issue #314: Fixed a bug that prevented the retry mechanism from working properly.
- Issue #316: Disabling rebase for objects with +2 errors.
- Issue #318: Database validation now is optional.
- Issue #322: Fixed Xcode 6 CoreData Threading Warnings.
- Issue #324: Fixed an invalid CoreData context mapping.
- Issue #326: Preventing empty CV scenarios.
- Issue #328: Fixing tabs. Updated initializers all over.