Add test for each app
Changes to the other SNAPPY libraries could break the demo apps, if any of the functions change, which might not be discovered until someone tries to use it. For example, I just got an error in the sksurgeryrendermodelslikecamera app when I tried to run it (looks like one of the fuctions it uses has been renamed).
We should add a simple test for each app (i.e. does it run OK), and encourage people to implement tests for new apps when they make them.