Bootstrap QGLViewer as vendor library for usage by g2o

[paul-michalik]

Continuing work on a task INTHAD-188:

Scenario: Bootstrap a vendor package
    As a developer I want to add vendor packages
    which are not delivered via official channels (vcpkg, ...)
    And which for some reason should not be distributed via official package delivery channels
    In order to use them in my project and share the setup with my team

The first sketch is to add a vendor section to bootstrap.bat or bootstrap.sh which installs the required packages into .vendor folder. In the structure of the vendor folder will follow the conventions and layout of vcpkg folders.

The issue has two purposes:

• We are working towards the notion of a "workspace" which is used to develop software on one developer box. In such a workspace, there would be one .vcpkg (or vcpkg.io) folder, one .vendor (or .vendor.io) folder. All projects are located inside a workspace following a set conventions. Inspiration: golang workspaces, catkin workspaces, and many more.
• We want to demonstrate/learn how to use the vcpkg driven installation of Qt and its toolchain to build Qt based project

[paul-michalik]

Please continue the development on feature/#11-bootstrap-qglviewer-as-vendor-library-for-usage-by-g2o.