Enable running multiple versions of PoshBot side-by-side

[Tadas]

This makes PoshBot more "portable" and makes it possible to run multiple versions side-by-side

Description

Instead of relying on Import-Module PoshBot to load a module found via $env:PSModulePath we explicitly specify which module manifest to load. That way you can have PoshBot installed in your system while also working on a newer version.

Related Issue

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [x] All new and existing tests passed.

[devblackops]

Thanks @Tadas! I ran through some tests and this looks good to me. Even exposed an unrelated bug which I'll be fixing 🐛