Correctly unwrap optionals in C4View
Correctly unwrap optionals in C4View

There was a bug where optionals where not being unwrapped properly
resuting in views passed in as optionals not being added as subviews.
Also add a fatalError when trying to add something that is not a view as
subview. Fix #333

C4Labs/C4iOS,C4Labs/C4iOS,C4Framework/C4iOS,C4Framework/C4iOS