Unitl now, we didn't have any software that needed to be built from
source. But Gnuastro is one software that users of this system will
regularly be using and it was important to install the latest version
from source. Also, another commonly necessary software in astronomy is
TOPCAT.

With this commit, Gnuastro's steps have been added to the new user
setup script (which needed editing of the bashrc files) and TOPCAT is
now also installed.