Added POT generator

General comments:
Sorry it took me so long to get back into this. I saw the commit a couple weeks ago for the new parser so I've updated and repushed the Visual Studio plugin for generating the POT files.

About this push request:
Added VS package that allows to generate POT on-demand from the solution
explorer. It uses the same strategy as the new parser, based on web.config settings.
I also had to sign the i18n.Domain project so it could be referenced inside the POT generator.

I also think this makes debuging the parser A LOT simpler as you can debug it from within the POTGenerator without the need to manuall input arguments into the postbuild to match a project you want to test againts.

TODOs:
+ Use a single key to sign all i18n projects
+ Add POT Generator package to nuget so it will be installed when i18n is installed
+ Add documentation about the plugin to general documentation file