Restructure page locations and form flow

This implements Anne-Sophie's revised site designs from: https://bugs.caret.cam.ac.uk/browse/PAVO-175

The previous contents of /me are show shown on the home (/) page when logged in. When logged out the home page shows the previous info content.

The form is now @ /upload. The file is uploaded as a content item before the main form is presented.
They're not there as an optimisation to avoid querying twice, they're there to name element(s) to make the code clearer, and to a lesser extent to list the elements in one place. Also `$successContainer` is referenced twice. (Yes, you could combine the two, but I think it's best not to.)