GSoC Phase 2: K12 building phase

What this merge request does

• On Windows, create desktop and Start Menu shortcuts that starts Purr Data in K12 Mode.
• On Mac, create a minimal K12 Launcher in the .dmg that starts Purr Data in K12 Mode. The user needs to put the launcher in the same directory as the Purr Data app.
• Prepare icons and a list for the K12 abstractions.

(No changes to the Linux building phase since it's already taken care of by Pd-l2ork 1.0.)