Move user requested apt-get packages to be installed into starter.ini

[apolopena]

Currently packages the user wants downloaded during the image build step are in set as a string in .gp/bash/install-project-packages.sh but that string should really be parsed from starter.ini so .gp/bash/install-project-packages.sh can remain untouched since there is core logic in that files that could change in a future release.

Add a new section to starter.ini for packages that should be installed during the docker image build phase. The valid value will be a space delimited string of valid apt-get packages with no trailing or leading space.

[apt-get]
packages=