(#12) Install multiple packages at once

[lukasxcs]

Description Of Changes

Ability to select and install multiple packages at once by highlighting each, and clicking an "Install Selected" button on top

Motivation and Context

Basic functionality, simple to implement

Testing

Tested myself but have not written any tests

Operating Systems Testing

Windows 11

Change Types Made

• Bug fix (non-breaking change).
• Feature / Enhancement (non-breaking change).
• Breaking change (fix or feature that could cause existing functionality to change).
• Documentation changes.
• PowerShell code changes.

Change Checklist

• Requires a change to the documentation.
• Documentation has been updated.
• Tests to cover my changes, have been added.
• All new and existing tests passed?
• PowerShell code changes: PowerShell v3 compatibility checked?

Related Issue

#12