check if required binaries are on PATH before continuing with (un)install process

[andrewazores]

📝 Description

Adds precondition checks to the install.sh and uninstall.sh to ensure that required commands are on the $PATH.

📑 Context

If these commands are not on the $PATH then the installation or uninstallation process will begin and then fail part way through in an inconsistent state. It is better to require the user to install all prerequisites first, so the script behaviour is easier to reason about (more atomic) as well as failure modes may be more clearly explained to the user.

✅ Checklist:

• [ ] Updated tests for this change.
• [x] Tested the changes locally.
• [ ] Updated documentation.
• [x] Change version number.
• [ ] Change the time and date.

[andrewazores]

@cryinkfly I'm not sure what tests and documentation updates may be needed here, and I'm not sure about the version number or time/date expectations either. Hopefully this change is minimally invasive enough and self-evident enough for a painless review despite these omissions.

[cryinkfly]

@andrewazores Thank you for your extra function to check if "YAD" is installed or no. :+1: