Ensure minimal project structure

[abingham]

Camtasia project JSON has a lot of "optional" parts. For example, if you don't have any timeline markers, you don't necessarily have an empty list in the JSON...you might be missing the entire subtree that holds that list. This makes some of our access code a bit messy.

How can we simplify things?

One option is to "normalize" the project before we use it. We would just inject the missing skeleton before we do anything with the project. Then all parts of code that use the JSON struct could rely on a certain minimal structure.