Selection system

Tilføjet et system til valg af modul, så man kan vælge et system og
vende tilbage til hovedmenuen, når der ønskes et andet.
Added clr-screen and number select for the system

puts "\e[H\e[2J" added to clear the screen at strategic points in the
application.

References to the system and back has been added.
Just my little strategy. To be continued.