Add dependency checks on launch

[mithusingh32]

I think this is a potential enhancement to have the script check for dependencies, particularly zenity.

I'm running on Neon LTS, and zenity is not installed. Took my a few minutes realize why the script was not working. I think having a clear message on launch like "Zenity not detected! Exiting launcher"

I'm not proud it took me so long to discover that since all i got from terminal was "zenity: command not found" and that didn't automatically trigger "Oh im missing a dependency"

I also think exiting on ANY Failure might be a good idea too. (Adding set -e to the top of script or just having checks to perform any rollback if necessary)

[moraroy]

@mithusingh32 will look into fixing this thank you!