Pip to Pipx switch

[vxbinaca]

We could make a step 0 or re-order all the main steps to remove the old Tubeup installs with a one line command if you'd like, would prob be a good idea.

Advanteges of PipX over Pip:

• Pipx handles creating a virtual environment thats sandboxed from the system python installation which is MUCH safer to do.
• One line packages upgrade for anything in the sandbox
• Allows internetarchive to run old versions of urllib or whatever it needs while tubeup can advance to fresher versions of packages with no conflicts or dependency hell
• Pipx doesn't need root privileges to install new packages, good for people on a VPS where they don't have root.
• PEP 668 compliant, and non-compliance is a train that will come down our tracks sooner rather than later.

Disadvantages:

• Users will need to uninstall their current install of tubeup and internetarchive, which I can do in a patch to this PR or after after merge

[vxbinaca]

I should add the user may not have to reconfigure IA because of the locations of it's config files. You'd just unplug it from the system install and when IA gets plugged back into the virtual-env it should pick the configs back up.

[vxbinaca]

I have to merge this because it A) Needs to be done for PEP 668 compat in the future, and because I need to make another change to the README and this will. Others have had a month to review and comment. Times up.