Fixed layout issues.
Fixed layout issues.

linear node sequnce gui element now appears in the center of the screen instead of the center of the tree.

hjanime/VisTrails,celiafish/VisTrails,minesense/VisTrails,celiafish/VisTrails,hjanime/VisTrails,Nikea/VisTrails,minesense/VisTrails,Nikea/VisTrails,minesense/VisTrails,minesense/VisTrails,celiafish/VisTrails,celiafish/VisTrails,hjanime/VisTrails,hjanime/VisTrails,Nikea/VisTrails,VisTrails/VisTrails,VisTrails/VisTrails,VisTrails/VisTrails,minesense/VisTrails,hjanime/VisTrails,VisTrails/VisTrails,Nikea/VisTrails,VisTrails/VisTrails