Add feature for the PG open hidden without prompt window

[Leandro-Reis]

Read that the issue session isn't only for issues but for ideas as well. I've been using this portable version of PG for my personal project. Would be nice if it could be started without any windows showing completely hidden. For my application this would be nice because i'm developing a content manager that works directly from an usb drive for my use only and i don't want the prompt window showing alongside with my main app, anyway, it is just an idea. Congratulations for this awesome portable version of PG.