Remove custom installer, create setup.py

[ghost]

Historically, GAM has shipped with a custom installer script. With all of this great work to split up the project into smaller modules, it behooves the project to also include a proper setup.py.

[jay0lee]

Most GAM admins utilize the custom installer today. It ensures they are getting the latest version of Python, OpenSSL and Python libraries without the admin needing to install and maintain any of the above. In short, the custom installer is not going anywhere.

I'm not opposed to a setup.py / GAM being pip-installable but it has not been high enough priority for me to carry out. PRs always welcomed.

[ghost]

The admin should have to install their own Python, OpenSSL, and Python libraries. It's not okay for one userspace application to dictate OS versions and just start mucking around with internals like that. Instructions in a readme file of what prerequisites are needed offer a clear advantage by removing this project's responsibilities of the admin's machines and removing custom code. As it stands, there's a very difficult-to-read installation script clocking in at 375 lines - 202 of which are raising bugs in shellcheck.

[ghost]

Case in point, install-gam.sh does not set set -e or set -u, so errors/unset variables will be ignored. Line 220 has temp_archive_dir=$(mktemp -d 2>/dev/null || mktemp -d -t 'mytmpdir'). If at any point that command outputs nothing or an error (e.g. a typo in a commit that updates the line), then the program will happily move along. The end of the file has trap "rm -rf $temp_archive_dir" EXIT, which will rm -rf a potentially unset variable. GAM is now liable for the possibility of wiping out a user's home directory in entirety.

It's an unlikely scenario, but has happened before. This could be easier to maintain and safer if it used standard Python packaging rather than going its own road for no gain.

[jay0lee]

This is actually a dupe of #720. Again, PRs are always welcome.