update_system ==> aptget_stuff

-Moved update_system’s contents to aptget_stuff
-Calling aptget_stuff without arguments updates & upgrades packages
-Added and edited Strings
-Added and edited comments
Minor adjustments

-Minor adjustment in $Err color presentation
-Edited Package Installation string
-Renamed $select… ==> $selected…
-Separated $projLink into $projLink and $selectedProj
Better install_sdl handling

-Better install_sdl handling (plus: it now asks you to wait)
-Added $tryAgain string
-wantedSDL ===> wantedSDLFile
-Better downloaded libs identifying method
-noSDL ===> noDledSDL
-Edited some comments