'views' setting for mounted apps should inherit from parent app

Attached a commit with a failing test case, and two commented out alternatives for making it pass. Option 1 is my preferred as it continues the behaviour we had in express 2.x. Option 2 would require a bit of documentation to make it clear that some settings are not inherited.

Option 1 would probably involve some thinking about which settings should be inherited. Perhaps they all should? I suspect that is what is wanted, in line with #426.