FEATURE - Run VSIXInstaller from the command line in silent mode with a custom progress dialog

[astrohart]

I've learned, while making setup scripts for my own machine, how to call VSIXInstaller.exe from the command line, i.e., from a .bat file, to make it silently and automatically install extensions.

I propose making this the default means by which this tool installs downloaded and selected extensions while displaying a custom progress dialog. This would reduce the need for user interaction during the process.