Better treatment of our subview properties (board and scoreView)
Better treatment of our subview properties (board and scoreView)

Make these properties weak as they are part of our view hierarchy, thus, ownership is established by inherited/contained properties (i.e. view.subviews). Also, make them implicitly unwrapped optionals to more simply express our requirements/expectations, instead of lots of asserts and forced unwrapping.

Also finish checking in (part of the change was wrongly staged into an earlier commit) the change for separating protocol conformance (GameModelProtocol) into an extension. Nice for dividing up the class implementation into conceptual blocks.

sanvital/swift-2048