Some minor polish for unicorn on iPhone / iPad.

Added following code FolderPickerViewController to keep images and folders only:
    //Getting the folder's childrens
    BoxCollectionBlock listSuccess = ^(BoxCollection *collection)
    {
        [self.customRefreshControl endRefreshing];

        self.totalCount = [[collection totalCount] integerValue];

        if (self.totalCount > self.items.count) {
            //Adding the page retrieved
            for (int i = 0; i < [collection numberOfEntries]; i++)
            {
                BoxItem *item =  (BoxItem *)[collection modelAtIndex:i];
                if ([item isKindOfClass:[BoxFile class]]) {
                    BoxFile *file = (BoxFile *)item;
                    NSString *extension = [file.name pathExtension];
                    if ([extension isEqualToString:@"png"] || [extension isEqualToString:@"jpg"]
                        || [extension isEqualToString:@"jpeg"] || [extension isEqualToString:@"JPG"]) {
                        [self.items addObject:item];
                    }

                } else ([item isKindOfClass:[BoxFolder class]]){
                    [self.items addObject:item];
                }
            }
        }

        dispatch_async(dispatch_get_main_queue(), ^{
            self.navigationItem.prompt = nil;

            [self.tableViewPicker refreshData];
        });
    };