Changed AdCreationManager to keep track of which stage we are in and handle going forward or backward in the funnel

Cleaned up the main page too, and modified the crop activity to work in the funnel. Works well so far!

Still need to modify the text and logo activities to work with the funnel.

There are some things we need to figure out with the undoing, right now it takes you to the previous activity but doesn't pop anything off the stack.