#3 Linear DS layout algorithm always put edges in the bottom

[BoC]

Currently when user click on, move or resize a linear
DS container vertex, or do other things that would
invoke the linear DS layout function, the vertices in
the linear DS will go to the top most, putting edges in
the bottom. I realized this problem when I first wrote
the linear DS layout function, but due to time
constraint did not fix it. It should be fixed soon.