Reindent and breaking change (shared/_header)

As promised, here is a pull request based on work I did on the plane.

Please, do NOT blindly merge it. You may be unpleasantly surprised. I did all this work without ever starting your app or running the tests, so there is no guarantee whatsoever that the app is working as well as it did before.

Look through the commit(s) and see what I changed, whether refactors, comments, deletions or reindentations. This pull request is the right place to start a conversation, so ask your questions here.