Add code for files extraction without gui

As freenetinstaller is a custom installer written in AutoHotKey embedded files can't be extracted without using the GUI.

Here are some lines of code that allow to extract (and not install) files in a "GUI less mod".
Calling Freenetinstaller.exe with the command line **/ExtractTo=** 

e.g : 
```
 Freenetinstaller.exe /ExtractTo="D:\Freenet"
```
will extract files without GUI.

This a "pure" extraction nothing is done to the system.

**Why this pull request ?**
Yes, this pull is "self-interested" . I'm currently working on an alternative launcher for Freenet with portability in mind. The project is open source and can be found [here](https://bitbucket.org/romnbb/freenetfortraveler/wiki/Home) (FreenetForTraveler)

Currently, the only way i found is to provide a zip of Freenet (state : after installation but before launch).

N.B: Until recently, FreenetForTraveler was only a "personal use" project but after some search and reading [this subject](https://freenet.uservoice.com/forums/8861-general/suggestions/113599-portable-freenet#comments) , maybe it can fill the needs of some others people.