Add a prompt option for Defaults

[ghost]

trafficstars

It might be useful to get user input during the installation of a module/application for the value of a variable to be used.

[daimor]

Don't think that interactive mode is a good way, due to most usage being automated installation, where no way to input anything But the values can be passed by -D parameter during install

[isc-tleavitt]

For backward compatibility I think the right approach would be adding an "interactive" flag for install/load that can be checked in package-specific code (with corresponding documentation). This should be done.