Allow per-user-installations

Some packages (like [nvs](https://chocolatey.org/packages/nvs)) are per-user installers and probably with good reason to be so.
However, chocolatey will track the installed package globally.

That means on a multi-user-system:
* UserA installs a package (say nvs) and all is fine for UserA
* UserB has no access to the installed package of UserA and additionally chcolatey aborts an installation due to the fact that the package is already installed.

I see two ways out of this:
* enabe chcolatey to deal with user-installers (additionally thouse might not need admin-privileges to install...)
* write a "wrapper" package so that only the installer get's installed (globally) and the per-user-installer get's started on first start for each user.

Any thoughts on this?

The issue names no files, tests, or entry points. First clarify how Chocolatey should track per-user installers, then compare native per-user support with the proposed wrapper package; done means separate users can install and use the same package without Chocolatey treating it as globally installed.

Written by the indexing model from the issue text.