Raspbian Support

[XavierChanth]

- What I did Added Raspbian support to getdess.sh
Closes #10

Cleaned up the scripts:

• Added an exit code function to provide some context to installation issues
• Used the correct color code for tput setaf
• Removed unused atsign.sh file (part of getdess.sh now)
• Fixed echo prompt texts

- How I did it

• Added raspbian and armv7l to the support lists
• Used shellcheck to find and fix shell issues
• Found and fixed the other issues manually

- How to verify it

• Pull and run getdess.sh from https://raw.githubusercontent.com/XavierChanth/dess/trunk/getdess.sh
• I verified on a raspbian 10, pi3 with atsign interiorwolverine using buzz

- Description for the changelog Add Raspbian support to getdess installer

[XavierChanth]

It should be fine as is for the previously supported OSs, nothing has fundamentally changed in terms of how they install.

All I did in terms of functional changes was add raspbian and armv7 to the support lists. The installer follows the same steps as arm64, the only difference is that we needed the armv7 docker image.

The non-functional changes I did:

Fixed colors for certain shells: 7 is the correct color code for white when using tput setaf <color-code> If you use 9, it will fallback to white on some shells, but red on others (like windows terminal for example).

Also did some globbing fixes for the variables in the other files, no commands have been changed. If it works on the pi, it should work on any other OS/arch, since these are platform agnostic commands that I was shellchecking.

The last change that I made was to the error_exit function, which was to unify all the error codes to a single place. The flow for non-zero exits has not changed, it has just been refactored to make working with non-zero exits easier to maintain.

[cpswan]

I did a quick test on an Amazon Linux instance, and LGTM