Add apt-get, moved package lists to variables

I added apt-get just in case aptitude is not available and move the
lists of packages to there own variables.
Change directory finding, Add another link path

I changed directory finding to make sure it will find the correct
directories for all linux distroes. For instance in Arch the SteamApps
directory is in STEAMROOT/Steam/SteamApps/ instead of
STEAMROOT/steam/SteamApps. I added another link path because the
required libraries can from from either of these directories. At least
that was the case in my script.
Merge pull request #13 from bubylou/master

Add apt-get, Moved package lists to variables, Change directory finding, Add another link path