* A simple and minimal fix of 4665 to check for the Visual Studio C++ 2015 redistributables. Note that this is specific to 2015 (vcruntime140.dll refers to the Visual Studio version 14.0, which maps to Visual Studio 2015).
A previous check registry check of 'SOFTWARE\Microsoft\DevDiv\VC\Servicing\14.0\RuntimeMinimum' failed because when the redistributables are installed via Windows update (which does not use MSI), then the registry entry did not get populated.
The 'Pending' attribute was removed from existing tests since the download links are now present again and the tests were improved using Pester TestCases.
* Fixed typo spotted in code review of PR 4745
* Remove DirectorySearch Id duplication by defining it once and referencing according to this special trick in the official WiX documentation here: http://wixtoolset.org/documentation/manual/v3/howtos/files_and_registry/directorysearchref.html
Renamed property values as suggested.
* Remove replacements of HTTPS with HTTP, i.e. test against exact link. Use -UseBasicParsing switch with the hope of not having failures in the CI environment.
Added comment why there is no assertion about the StatusCode.
* Replace download links with link to pre-requisites page as suggested in PR 4745 because this page is easier to update
* Compilation error CNDL0012 fix: WiX does not allow lowercase characters for file search property Ids because due to them being used for a search property means that they must be public, hence lowercase is not allowed.
* #4458 MSI installer checks that the Windows C Runtime and VS Studio 2015 C++ redistributables are present and returns error message if not.
Includes tests to check that the Wix file contains the download URLs and those URLs are not dead.
Added a checkbox (unchecked by default) to the last dialogue of the Windows installer to provide the option of opening PowerShell because that's what most people want to do if they installed PowerShell.
