Limit white liner to max tracks only

[anytizer]

For some aesthetic/decorative reasons, the vertical white liner should be limited to the max height of the tracks only. Currently, it goes too below until the screen or track area ends.

When a new track is added or removed, the height should adjust by the space occupied by the new change.

[mrf7777]

I think that this is a good issue for me, and I would like to work on it.