do not resume cancelled downloads on restart

core/src/main/groovy/com/muwire/core/Core.groovy

@@ -12,6 +12,7 @@ import com.muwire.core.connection.I2PConnector
 import com.muwire.core.connection.LeafConnectionManager
 import com.muwire.core.connection.UltrapeerConnectionManager
 import com.muwire.core.download.DownloadManager
+import com.muwire.core.download.UIDownloadCancelledEvent
 import com.muwire.core.download.UIDownloadEvent
 import com.muwire.core.files.FileDownloadedEvent
 import com.muwire.core.files.FileHashedEvent
@@ -195,6 +196,7 @@ public class Core {
         eventBus.register(UIDownloadEvent.class, downloadManager)
         eventBus.register(UILoadedEvent.class, downloadManager)
         eventBus.register(FileDownloadedEvent.class, downloadManager)
+        eventBus.register(UIDownloadCancelledEvent.class, downloadManager)
         
         log.info("initializing upload manager")
         UploadManager uploadManager = new UploadManager(eventBus, fileManager)

core/src/main/groovy/com/muwire/core/download/DownloadManager.groovy

@@ -68,6 +68,11 @@ public class DownloadManager {
         eventBus.publish(new DownloadStartedEvent(downloader : downloader))
     }
     
+    public void onUIDownloadCancelledEvent(UIDownloadCancelledEvent e) {
+        downloaders.remove(e.downloader)
+        persistDownloaders()
+    }
+    
     void resume(Downloader downloader) {
         executor.execute({downloader.download() as Runnable})
     }

core/src/main/groovy/com/muwire/core/download/UIDownloadCancelledEvent.groovy

@@ -0,0 +1,7 @@
+package com.muwire.core.download
+
+import com.muwire.core.Event
+
+class UIDownloadCancelledEvent extends Event {
+    Downloader downloader
+}

gui/griffon-app/controllers/com/muwire/gui/MainFrameController.groovy

@@ -15,6 +15,7 @@ import javax.inject.Inject
 import com.muwire.core.Constants
 import com.muwire.core.Core
 import com.muwire.core.download.DownloadStartedEvent
+import com.muwire.core.download.UIDownloadCancelledEvent
 import com.muwire.core.download.UIDownloadEvent
 import com.muwire.core.search.QueryEvent
 import com.muwire.core.search.SearchEvent
@@ -133,6 +134,7 @@ class MainFrameController {
     void cancel() {
         def downloader = model.downloads[selectedDownload()].downloader
         downloader.cancel()
+        core.eventBus.publish(new UIDownloadCancelledEvent(downloader : downloader))
     }
     
     @ControllerAction