Fix bug in to/from_string methods
Fix bug in to/from_string methods

Add class as first argument

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