Xcode 6.1 support, remove RBLView

`RBLView` makes too many choices for you, and `NSView` offers largely similar functionality in 10.10 now.

~~The unit tests don't currently build, because Specta/Expecta haven't yet been updated for Xcode 6.~~
XCTest is stricter than OCUnit about doing GUI things. Opening a window crashes the runner.