split gitit2 subsite from gitit2 master application

http://stackoverflow.com/questions/30267487/scaffolding-and-workflow-for-a-yesod-sub-site

The Yesod Scaffolding proposes to put the main part of an application in a library, but cabal can only handle one library per cabal file.

So there should be one git project just with the subsite and another one that uses the subsite. It's easy to develop them in sync now that cabal offers sandboxes and the add-source command.