The Data Transfer Project is a new team-up between tech giants to let you move your content, contacts, and more across apps. Founded by Facebook, Google, Twitter, and Microsoft, the DTP today revealed its plans for an open source data portability platform any online service can join. While many companies already let you download your information, that’s not very helpful if you can’t easily upload and use it elsewhere — whether you want to evacuate a social network you hate, back up your data somewhere different, or bring your digital identity along when you try a new app. The DTP’s tool isn’t ready for use yet, but the group today laid out a white paper for how it will work…