Added VS2012 package for adding the post build task as a solution explor...

...er button. This will help decouple the POT generating process from the build process and hopefully make the process more transparent while retaining its ease of use

I've also moved the PostBuildTask out of i18 and into the PostBuild project as has been discussed

Now, I couldn't reuse this class inside the Package because it would have required to sign the assemblies and to move them to .net 4.5, which was a bit too much. So right now there is a little bit of code duplicated between those two PostBuildTask classes, but I definetely see those diverging more as time passes.

There is one major ToDo which is to be able to somehow embbed the gettext tools (or at least make their location configurable) so that they won't have to be in a specific route in your project/solution. I'm waiting on you and Martin for this as you said you were working on it.