Update RFChoiceField

Add distinctUntilChanged to visibleFields signal
Refactor RFForm not to send empty changes to observer
Clean up RFFormTableViewDataSource
Add RFEActionFieldController to example
Remove unused RFFieldMatcher category on NSPredicate
Update example view controller to use RFEActionFieldController
Update example view controller to use RFEActionFieldController
Expose fields opeartion methods in RFSection
Update RFFormContentProvider to use exposed methods
Update RFForm to use exposed methods
Update RFCollectionOperations

Add eachWithIndex, filterNot, filterNotEmpty
Update Unistream payment form