Adding close process and service stop to windows installer

Hi,

Here's a new version of the installer file.

* Now it cleans cache directory
* It stops salt-minion service before upgrading
* It closes salt-minion.exe process (needed if install is launched from salt).

But WARNING there's 2 drawbacks:
* You need to add nsProcess NSIS plugin
* Salt can't return when we close salt-minion process :-( but it's needed to upgrade salt-minion.exe

Regards
Pierre