Keep output of CLI installation command #628

As discussed in https://github.com/shanalikhan/code-settings-sync/issues/618#issuecomment-417201279, it would be useful to keep the output of extension installation, something like:

CODE SETTINGS SYNC - COMMAND LINE EXTENSION DOWNLOAD SUMMARY
Version: 3.1.0
------------------------
TOTAL EXTENSIONS : 3

"/usr/share/code/bin//code" --install-extension alefragnani.Bookmarks
Found 'alefragnani.Bookmarks' in the marketplace.
Installing...
Extension 'alefragnani.Bookmarks' v9.0.3 was successfully installed!

EXTENSION : 1 / 3 INSTALLED.

"/usr/share/code/bin//code" --install-extension msjsdiag.debugger-for-chrome

Currently, it is replaced by the final summary after a short while.