a lot of changes:
a lot of changes:

* added initial support for gui-less simulations
* removed certain static variables for robustness
* added support for standard gui plugins (startup)
* added quick-load menu option
* separated plugins from plugin visualizers

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