ADD: SelfShowableContent - a new kind of opening outcome

It is often used in conjuction with openers that do load-and-show
on their own, as opposite to load-only-and-have-Fiji-to-show pattern.

src/main/java/org/scijava/ui/SelfShowableContent.java

@@ -0,0 +1,42 @@
+package org.scijava.ui;
+
+import java.util.function.Consumer;
+
+/**
+ * Representation of an outcome after opening some input, be it a file on a drive, URL,
+ * object from a drag-and-drop event or alike. The outcome is represented with an object
+ * with the data itself, and a method that knows how to present (that means read and display)
+ * this data. The class is primarily intended for opening inputs which ImageJ2 is not normally
+ * able to open. Example of such opening outcomes are opening of a specific/proprietary data file
+ * for GUI-based applications such as BigDataViewer or Mastodon.
+ *
+ * @param <T> The particular type for the particular data.
+ *
+ * @author Curtis Rueden, Vladimir Ulman
+ */
+public class SelfShowableContent<T> {
+	private T content;
+	private Consumer<T> showAction;
+
+	/**
+	 * Binds together a particular piece of data and a method that knows how to open it.
+	 * @param content
+	 * @param showAction
+	 */
+	public SelfShowableContent(T content, Consumer<T> showAction) {
+		this.content = content;
+		this.showAction = showAction;
+	}
+
+	/** Getter of the stored data. */
+	public T content() {
+		return content;
+	}
+
+	/**
+	 * This starts the actual opening/consuming of the stored data.
+	 */
+	public void show() {
+		showAction.accept(content());
+	}
+}