Beta Build

Added functionality to build a beta release.
Added functionality to get the __piratebox-mod-imageboard__ from the __openwrt-piratebox-feed__ repo instead of wgetting the package.

Refactored the __image_helper.sh__ script a little bit.

Added some more information to the README.

I was wondering about the _infos_about_PirateBoxScripts.txt_ file. Does it belong to this Repo? Wouldn't it better fit in the PirateBoxScripts_Webserver repository?

Greetz,
Chris