Rewrite solution to cull bad configs/platforms, add single-VS options.

Also build Debug platforms for completeness.

Configurations:
  - Removed "Debug.Lab" and "Release.Lab" - these seem unnecessary.
  - Always build 'everything', instead of a weird hodge podge of missing
    projects for any given configuration.
  - Always build project configurations by the same name.

Platforms:
  - "Mixed Platforms" replaced with "All VS", which builds everything always.
  - New "VS2015 Only" builds everything but VS2017-specific projects.
  - New "VS2017 Only" builds everything but VS2015-specific projects.
  - "x86", "x64", and "Any CPU" are all removed.  We always want to build
    a mixture of "Any CPU" (most projects) and "x86" (setup projects.)

Closes PistonDevelopers#295
       "Clean up solution config/platform matrix."