Make DynamicCommand work when not in plugin index

This enables some new use cases: e.g. it becomes possible to make a
DynamicCommand anonymous subclass as a local variable in a method,
for the purpose of using it once, without registering it in the context.

Author: ctrueden

src/main/java/org/scijava/command/DynamicCommand.java

@@ -79,7 +79,8 @@ public abstract class DynamicCommand extends DefaultMutableModule implements
 	public DynamicCommandInfo getInfo() {
 		if (info == null) {
 			// NB: Create dynamic metadata lazily.
-			final CommandInfo commandInfo = commandService.getCommand(getClass());
+			CommandInfo commandInfo = commandService.getCommand(getClass());
+			if (commandInfo == null) commandInfo = new CommandInfo(getClass());
 			info = new DynamicCommandInfo(commandInfo, getClass());
 		}
 		return info;

src/main/java/org/scijava/command/DynamicCommandInfo.java

@@ -51,9 +51,9 @@
  * Helper class for maintaining a {@link DynamicCommand}'s associated
  * {@link ModuleInfo}.
  * <p>
- * The {@link CommandService} has a plain {@link CommandInfo} object in its
- * index, populated from the {@link DynamicCommand}'s @{@link Plugin}
- * annotation. So this class adapts that object, delegating to it for the
+ * This class wraps a plain {@link CommandInfo} object (e.g. from the
+ * {@link CommandService}'s index, present due to an @{@link Plugin} annotation
+ * on the {@link DynamicCommand} class), delegating to it for the
  * {@link UIDetails} methods. The plain {@link CommandInfo} cannot be used
  * as-is, however, because we need to override the {@link ModuleInfo} methods as
  * well as provide metadata manipulation functionality such as