installer configs and npm

[jeremy-seipelt]

I had some issues installing do to my use of npm instead of yarn.
I know you use yarn, but npm should be an acceptable drop in replacement, espacially because it works to a certain point.

Another really agonizing point during installation was always to reenter the installer parameters, and the need to remove the old backend folder which gets created but not removed when installation fails.

So my idea would be to allow an installer.json where the params can be static and something like an -f flag which allows overwriting an existing backend folder.

Maybe we could add npm as a fallback to yarn, because if you got node you probably got npm too and you dont need the additional dependency.