Clean up SDL Structs with a category on NSMutableDictionary

[justinjdickow]

Every setter method in every SDLRPCStruct subclass takes an object and sets it in the store. If the object passed into the method is nil, the object is removed from the store instead (because passing nil to setObject throws an NSInvalidArgumentException). This makes every setter look like

-(void) setNavigationText:(NSString*) navigationText {
    if (navigationText != nil) {
        [store setObject:navigationText forKey:NAMES_navigationText];
    } else {
        [store removeObjectForKey:NAMES_navigationText];
    }
}

This can be cleaned up by creating a category on NSMutableDictionary and including it in the SDLRPCStruct class. It would look like

- (void)setOrRemoveObject:(id)object forKey:(id <NSCopying>)key {
    if (nil != object) {
        [self setObject:object forKey:key];
    } else {
        [self removeObjectForKey:key];
    }
}

Then every setter can be reduced to

- (void)setNavigationText:(NSString *)navigationText {
    [store setOrRemoveObject:navigationText forKey:NAMES_navigationText];
}