removed dependency on visplugin class, instead referencing plugin visualizers via new plugin method getGUI()
removed dependency on visplugin class, instead referencing plugin visualizers via new plugin method getGUI()

+ sanity-check when restoring last cooja location

arurke/contiki,arurke/contiki,bluerover/6lbr,arurke/contiki,bluerover/6lbr,bluerover/6lbr,MohamedSeliem/contiki,bluerover/6lbr,MohamedSeliem/contiki,arurke/contiki,MohamedSeliem/contiki,bluerover/6lbr,arurke/contiki,MohamedSeliem/contiki,arurke/contiki,arurke/contiki,bluerover/6lbr,MohamedSeliem/contiki,MohamedSeliem/contiki,bluerover/6lbr,MohamedSeliem/contiki