Remove all references to "Labs" in the ./common/ folder

[Arlodotexe]

Background

The ./common folder contains the MSBuild, scripted and supplemental project infrastructure for Labs.

Soon, we'll move the ./common folder to a submodule so it can be used to build v8.0 of the Windows Community Toolkit.

The problem

Almost everything in the ./common folder has a hardcoded reference to Labs, which isn't suitable for infrastructure shared across multiple projects.

The solution

The word "Labs" needs to be either removed or replaced with a generic and apt name for where it's used. When finished, there should be no usage of the word "Labs" in the ./common folder.

[Arlodotexe]

A large amount of work towards this has been done in #360 and #369. Lingering issues are:

• Sample app needs to be rebrand-able Tooling-Windows-Submodule#19
• Remove Labs from the default namespace for new components #387