wixstdba: Add auto-launch option via 'AutoLaunch' variable.

[nickdademo]

Any feedback welcome on this PR.

A feature often requested that could be quite useful, e.g:

• https://stackoverflow.com/questions/39745742/how-to-launch-the-application-after-a-quiet-call-to-wix-burn-bootstrap
• http://windows-installer-xml-wix-toolset.687559.n2.nabble.com/How-to-force-to-launch-application-in-silent-install-mode-td4021727.html
• https://stackoverflow.com/questions/12823722/start-application-after-installation-using-wix-burn
• After new version is updated it doesn't launch app automatically vslavik/winsparkle#132

If accepted, perhaps WiX4 would be a better place for it?

Usage

Within bootstrapper .wxs Bundle:

<Variable Name="AutoLaunch" bal:Overridable="yes" Type="numeric" Value="0" />

When running bootstrapper:

BootstrapperInstaller.exe AutoLaunch=1

Auto-launching will not be performed if a restart is to be performed.

[dnfclas]

All CLA requirements met.

[barnson]

This should go into WiX v4 first but should start with a thread on wix-devs: Triage was concerned about the name AutoLaunch as not being clearly to control this feature.

[nickdademo]

@barnson Do I need to create this thread on wix-devs? Or is it something the WiX team will do?

[robmen]

Consider moving to WiX v5 (when development starts).