Add ability to import previous cases

[komollo]

Issue:
Open Case Builder assumes that the user will start and finish a case within one session. The user was unable to save work and restart it later on. The user was also unable to load a case built with a prior version of Open Case Builder within the newest version of Open Case Builder.

Recommendation from Design Team:
Open Case Builder should have some kind of save state, or a system for saving and loading work-in-progress cases. Backwards compatibility may also be helpful.

[komollo]

This would require a lot of development work and adds much more complexity to technical design. That cannot be fixed in near future (in winter or spring) based on our current capacity. We can note in instructions for now. It may be possible to assign someone to this in the summer or fall.