Add ViewConfigurator

Sources/CollectionView/ViewConfigurator.swift

+import UIKit
+
+public struct ViewConfigurator<View: UIView, Model> {
+  public init(configure: @escaping (View, Model) -> Void) {
+    self.configure = configure
+  }
+
+  public var configure: (View, Model) -> Void
+
+  public func callAsFunction(view: View, with model: Model) {
+    configure(view, model)
+  }
+}
+
+#if DEBUG
+extension ViewConfigurator {
+  public static func failing() -> ViewConfigurator {
+    ViewConfigurator { _, _ in fatalError("Not implemented") }
+  }
+}
+#endif