Prevent git clone / wget issues during re-run of install.sh

[bwenrich]

Addresses #12 and some comments from https://groups.google.com/g/pidp-10/c/csbzz40gSQA/m/fwibojMWAQAJ

Minor installer improvements:

• Removes the destination folder for git clone of https://github.com/rcornwell/pidp10 if it already exists. Resolves an error that happens if you re-run the installer script.
• Changes the syntax for wget to prevent multiple copies of the file from accumulating if you re-run the installer script.
• Resolves a syntax error caused by --> in an unquoted string. This was an issue because it is interpreted by the shell as an output redirection.
• Combines multiple package installs which happen in a row. This should make the installation slightly faster & less chatty.

Cosmetic changes:

• standardizes apt syntax: -y install vs install -y
• cleans up whitespace, newlines, etc

Open Questions:

• Sometimes we are using apt and sometimes apt-get - not sure if this is intentional
• There are technically some undeclared dependencies in this script. If this is intended for RasPi OS & these are provided by default, perhaps it's not a problem. I only found this because my test environment is a minimal Ubuntu container.
  • wget
  • unzip
  • setcap (provided by libcap2-bin in Ubuntu)
• The same issue with git clone may also happen with https://github.com/PDP-10/its.git

[rcornwell]

He does not need to clone my repository, he can merge it into his. So perhaps this PR should wait until he merges in my PR.

[obsolescence]

Done! Forgive me, I manually redid your changes as I didn't see in time that you actually submitted them. But they're all in. Thank you!

[bwenrich]

Thanks for the suggestions. Due to the other in-progress changes, I have removed my updates related to the git clone duplicate folders.

Remaining fixes as described in the original PR comment are still present.

[rcornwell]

Personally I don't see any need to clone my repository. The panama code is about 2 years old and is missing many bug fixes since then. My sims repository is a development repository so there might be changes there that could break the simulator. This is why I don't copy all changes to open-simh right away. I have no problem maintaining second repository and pushing changes down as they pass testing.