implemented list_installed (Part of issue #1189)
implemented list_installed (Part of issue #1189)

berezovskyi/nikola,immanetize/nikola,schettino72/nikola,xuhdev/nikola,immanetize/nikola,wcmckee/nikola,wcmckee/nikola,xuhdev/nikola,JohnTroony/nikola,schettino72/nikola,schettino72/nikola,lucacerone/nikola,techdragon/nikola,andredias/nikola,masayuko/nikola,yamila-moreno/nikola,jjconti/nikola,jjconti/nikola,berezovskyi/nikola,atiro/nikola,andredias/nikola,jjconti/nikola,techdragon/nikola,pluser/nikola,getnikola/nikola,TyberiusPrime/nikola,JohnTroony/nikola,wcmckee/nikola,yamila-moreno/nikola,s2hc-johan/nikola,lucacerone/nikola,getnikola/nikola,okin/nikola,x1101/nikola,getnikola/nikola,immanetize/nikola,andredias/nikola,knowsuchagency/nikola,pluser/nikola,x1101/nikola,TyberiusPrime/nikola,pluser/nikola,s2hc-johan/nikola,masayuko/nikola,gwax/nikola,okin/nikola,xuhdev/nikola,yamila-moreno/nikola,x1101/nikola,getnikola/nikola,lucacerone/nikola,okin/nikola,gwax/nikola,gwax/nikola,atiro/nikola,okin/nikola,knowsuchagency/nikola,TyberiusPrime/nikola,atiro/nikola,masayuko/nikola,knowsuchagency/nikola,xuhdev/nikola,berezovskyi/nikola,JohnTroony/nikola,techdragon/nikola,s2hc-johan/nikola