Purge the imagej-legacy dependency

We can check whether the application frame is a UIComponent,
then check whether its associated component is a Frame,
without having a hard dependency on the LegacyApplicationFrame.
This reduces labkit-ui's dependency footprint, and avoids downstream
issues with the too-late patching of net.imagej:ij that can occur in
some scenarios when imagej-legacy is on the classpath.

pom.xml

@@ -174,10 +174,6 @@
 			<groupId>net.imglib2</groupId>
 			<artifactId>imglib2-algorithm</artifactId>
 		</dependency>
-		<dependency>
-			<groupId>net.imagej</groupId>
-			<artifactId>imagej-legacy</artifactId>
-		</dependency>
 		<dependency>
 			<groupId>net.imglib2</groupId>
 			<artifactId>imglib2</artifactId>

src/main/java/sc/fiji/labkit/ui/LabkitFrame.java

@@ -31,7 +31,6 @@
 
 import io.scif.services.DatasetIOService;
 import net.imagej.Dataset;
-import net.imagej.legacy.ui.LegacyApplicationFrame;
 import org.scijava.ui.ApplicationFrame;
 import org.scijava.ui.UIService;
 import org.scijava.widget.UIComponent;
@@ -113,11 +112,14 @@ private Image getImageJIcon(Context context) {
 			// NB: get ImageJ icon form the main UI window
 			UIService uiService = context.service(UIService.class);
 			ApplicationFrame applicationFrame = uiService.getDefaultUI().getApplicationFrame();
-			if (applicationFrame instanceof LegacyApplicationFrame)
-				return ((LegacyApplicationFrame) applicationFrame).getComponent().getIconImage();
+			Frame frame = null;
 			if (applicationFrame instanceof Frame)
-				return ((Frame) applicationFrame).getIconImage();
-			return null;
+				frame = (Frame) applicationFrame;
+			else if (applicationFrame instanceof UIComponent) {
+				Object uic = ((UIComponent) applicationFrame).getComponent();
+				if (uic instanceof Frame) frame = (Frame) uic;
+			}
+			return frame == null ? null : frame.getIconImage();
 		}
 		catch (Exception e) {
 			return null;