Adding flag to allow you to list out the opt-ins

[xtreme-steve-elliott]

Based on feedback from #300 this is PR simply adds the ability to list out available opt-ins using the --list flag to setup.sh. I had it check for the flag before the script runs sudo -K because listing out the options would not require admin and wouldn't actually be installing anything. If it is preferred that it runs after the analytics are turned on / off then I can rearrange some of the code to allow for that.

In my view, the only potential more-complicated-than-it-perhaps-needs-to-be part is the has_param method, which I have to allow for alternate flags (long and compact forms if desired in future), because I was tossing around the idea of allowing a compact flag like -l as an alternative to --list.