core: fix processing same class several times (#274)

Caution: This change can increase memory usage!
However overall decompilation must be faster

jadx-gui/src/main/java/jadx/gui/JadxWrapper.java

@@ -52,6 +52,8 @@ public class JadxWrapper {
 						Thread.sleep(500);
 					}
 					progressMonitor.close();
+					LOG.info("decompilation complete, freeing memory ...");
+					decompiler.getClasses().forEach(JavaClass::unload);
 					LOG.info("done");
 				} catch (InterruptedException e) {
 					LOG.error("Save interrupted", e);

jadx-gui/src/main/java/jadx/gui/treemodel/JClass.java

@@ -51,6 +51,7 @@ public class JClass extends JLoadableNode {
 	public synchronized void load() {
 		if (!loaded) {
 			cls.decompile();
+			cls.unload();
 			loaded = true;
 		}
 		update();