Added Version Checker integration

This PR adds integration with Version Checker (http://www.minecraftforum.net/topic/2721902-172version-checker). This is a small mod giving users a list of outdated mods, with options to easily update.

This adds a simple IMC message to Version Checker, which will then handle everything automatically. This does not create a dependency! The update message at startup is not shown when the IMC message has successfully been sent.

Preferably we should use a direct link to the new mod file, but I first need to know if this is something you want and what the best way is to get this link. This will allow users to update with a click on a button and a restart!

I know the 1.7 branch isn't finished yet (and both the edited files have errors), but it would be nice to have integration when the first 1.7 build is released :) 
yes, please use StringBuilder instead