Make TargetPlatformVersion and MInimumPlatformVersion configuable

As new versions of windows come out, our sliding window of supported versions needs to shift with it. (minor versions, like : 10.0.10586.0)

We need to make these values configurable via config.xml so developers don't have to dig through jsproj files.

A detailed explanation of the version history can be found here:

https://docs.microsoft.com/en-us/windows/uwp/updates-and-versions/choose-a-uwp-version

Discuss thread here:

http://markmail.org/message/tteqtdsksz2bbpdp