Add option to specify a local directory for all required installers

[UtahDave]

Add option to specify a local directory for all required installers

This is to avoid having to download everything from the internet every time.

[polliard]

I actually just created a build.ps1 that executes the build steps and broke the first script into a prepareEnvironment. That way I could pass into the build.ps1 a tag or branch string to change the build.