Highlighted link not always the correct link

[jerrymao15]

When components are added based on a state change, the correct link may not highlight/animate. It always seems to be the last link of the tree. This is because the way we are updating the links are based on IDs assigned from D3's tree methods. In order to fix this, we need to come up with another way of assigning IDs for D3 to use, or find another way to determine what links are new.