Updating podspec to include Core, Networking, CoreData, Operation, UI and Misc subspecs by default
Supports advanced sectionning in CLArrayController

* Adding concept of sectionKey used to uniquely identify section
* Sections can now be sorted using sectionsSortDescriptors
* Objects are sorted within sections rather than once globally
Support background rearranging in CLArrayController

* Replace rearrangeSignal with isRearranging BOOL