Allow copy action for chat messages

CopyMenuCollectionViewCell

- (BOOL)collectionView:(UICollectionView *)collectionView shouldShowMenuForItemAtIndexPath:(NSIndexPath *)indexPath
{
  return YES;
}

- (BOOL)collectionView:(UICollectionView *)collectionView canPerformAction:(SEL)action forItemAtIndexPath:(NSIndexPath *)indexPath withSender:(id)sender
{
  return action == @selector(copy:);
}

- (void)collectionView:(UICollectionView *)collectionView performAction:(SEL)action forItemAtIndexPath:(NSIndexPath *)indexPath withSender:(id)sender
{
  FLMessage* msg = self.fetchController.fetchedObjects[indexPath.row];
  UIPasteboard *pasteBoard = [UIPasteboard pasteboardWithName:UIPasteboardNameGeneral create:NO];
  pasteBoard.persistent = YES;
  pasteBoard.string = msg.text;
}