Fixed LinkTextTouchAttributes Bug

Fixed a bug where LinkTextTouchAttributes would be ignored if
LinkTextAttributes clashed.

For example if you set the LinkTextAttributes to: `@{NSForegroundColorAttributeName : [UIColor blueColor]}` and the LinkTextTouchAttributes to `@{NSForegroundColorAttributeName : [UIColor orangeColor]}` the link would stay blue even when tapped. The code I've added makes sure the LinkTextAttributes are removed when the link is tapped and then added again when the touch has finished.