Kronusdark/fix warnings

This pull request fixes two static analyzer warnings.

1. resignFirstResponder must include a call to super. [reference] (https://developer.apple.com/library/IOs/documentation/UIKit/Reference/UIResponder_Class/index.html#//apple_ref/occ/instm/UIResponder/resignFirstResponder)

2. If, for some reason field is nil in - (void)moveFieldAtIndex:(NSUInteger)index1 toIndex:(NSUInteger)index2, it will cause a call to -addObject: with a nil parameter which is a misuse of the API. [reference] (https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Classes/NSMutableArray_Class/#//apple_ref/occ/instm/NSMutableArray/addObject:)