Bug 1074117 - Use expected conditions and optimise element lookups in camera app object

As explained in IRC:

> davehunt: Bebe: wait_for_not_displayed is the exception for now
davehunt: there's no good alternative if the element has never been seen before
Bebe: aha
davehunt: Bebe: trust me, I want to get rid of those too, and will where I can easily
Bebe: oki
davehunt: a good example where I can get rid of it is find element a, click element b, wait for element a to be not displayed
davehunt: but if element a might never have been found before, we have a problem.. there's an open bug to improve the expected condition here