Manifest and cli

[keynmol]

1. Add a CLI module that allows installing dependencies into the managed locations from CLI

   • The purpose of it is being able to manage your vcpkg dependencies without having to fully load the build
   • This can be helpful because you can list your dependencies as just a call to scala-vcpkg command, run it in the container, and cache that layer - subsequent run of the SBT build will find everything already installed

2. Basic support for manifest files - they're installed along with the dependency list.

Closes #47