Add feature to create a single installer

Select multiple packages in gui and then make a single file that installs chocolatey and selected packages when run. I would love to see something like this implemented in the future. This would make my job so much better at work instead of using Ninite. This software is easier to integrate with other scripts.

The issue names no files, tests, or entry points. Start by locating the GUI flow for selecting multiple packages and the existing installation or export functionality. Done means defining and implementing a single runnable file that installs Chocolatey and the selected packages, with behavior confirmed for a representative selection.

Written by the indexing model from the issue text.