Add more hooks for podcasts/episodes

Add the following hooks in hooks.py:

 - on_podcast_subscribe
 - on_podcast_update_failed
 - on_podcast_delete
 - on_episode_delete
 - on_episode_remove_from_podcast

Call them as appropriate (in model.py)

src/gpodder/hooks.py

@@ -117,6 +117,14 @@ class HookManager(object):
     # the same function defined in them. If the handler functions here contain
     # any code, it will be called after all the hooks have been called.
 
+    @call_hooks
+    def on_podcast_subscribe(self, podcast):
+        """Called when the user subscribes to a new podcast feed.
+
+        @param podcast: A gpodder.model.PodcastChannel instance
+        """
+        pass
+
     @call_hooks
     def on_podcast_updated(self, podcast):
         """Called when a podcast feed was updated
@@ -127,6 +135,16 @@ class HookManager(object):
         """
         pass
 
+    @call_hooks
+    def on_podcast_update_failed(self, podcast, exception):
+        """Called when a podcast update failed.
+
+        @param podcast: A gpodder.model.PodcastChannel instance
+
+        @param exception: The reason.
+        """
+        pass
+
     @call_hooks
     def on_podcast_save(self, podcast):
         """Called when a podcast is saved to the database
@@ -138,6 +156,14 @@ class HookManager(object):
         """
         pass
 
+    @call_hooks
+    def on_podcast_delete(self, podcast):
+        """Called when a podcast is deleted from the database
+
+        @param podcast: A gpodder.model.PodcastChannel instance
+        """
+        pass
+
     @call_hooks
     def on_episode_save(self, episode):
         """Called when an episode is saved to the database
@@ -176,3 +202,18 @@ class HookManager(object):
         """
         pass
 
+    @call_hooks
+    def on_episode_delete(self, episode, filename):
+        """Called just before the episode's disk file is about to be
+        deleted."""
+        pass
+
+    @call_hooks
+    def on_episode_removed_from_podcast(self, episode):
+        """Called just before the episode is about to be removed from
+        the podcast channel, e.g., when the episode has not been
+        downloaded and it disappears from the feed.
+
+        @param podcast: A gpodder.model.PodcastChannel instance
+        """
+        pass

src/gpodder/model.py

@@ -405,6 +405,8 @@ class PodcastEpisode(PodcastModelObject):
     def delete_from_disk(self):
         filename = self.local_filename(create=False, check_only=True)
         if filename is not None:
+            if gpodder.user_hooks is not None:
+                gpodder.user_hooks.on_episode_delete(self, filename)
             util.delete_file(filename)
 
         self.set_state(gpodder.STATE_DELETED)
@@ -1012,6 +1014,8 @@ class PodcastChannel(PodcastModelObject):
             for episode in episodes_to_purge:
                 logger.debug('Episode removed from feed: %s (%s)',
                         episode.title, episode.guid)
+                if gpodder.user_hooks is not None:
+                    gpodder.user_hooks.on_episode_removed_from_podcast(episode)
                 self.db.delete_episode_by_guid(episode.guid, self.id)
 
                 # Remove the episode from the "children" episodes list
@@ -1067,6 +1071,8 @@ class PodcastChannel(PodcastModelObject):
             #feedcore.NotFound
             #feedcore.InvalidFeed
             #feedcore.UnknownStatusCode
+            if gpodder.user_hooks is not None:
+                gpodder.user_hooks.on_podcast_update_failed(self, e)
             raise
 
         if gpodder.user_hooks is not None:
@@ -1075,6 +1081,8 @@ class PodcastChannel(PodcastModelObject):
         self.db.commit()
 
     def delete(self):
+        if gpodder.user_hooks is not None:
+            gpodder.user_hooks.on_podcast_delete(self)
         self.db.delete_podcast(self)
 
     def save(self):
@@ -1082,6 +1090,9 @@ class PodcastChannel(PodcastModelObject):
             self.get_save_dir()
 
         if gpodder.user_hooks is not None:
+            if self.id is None:
+                gpodder.user_hooks.on_podcast_subscribe(self)
+
             gpodder.user_hooks.on_podcast_save(self)
 
         self.db.save_podcast(self)
@@ -1210,6 +1221,12 @@ class PodcastChannel(PodcastModelObject):
 
     def remove_downloaded(self):
         # Remove the download directory
+        if gpodder.user_hooks is not None:
+            for episode in self.get_downloaded_episodes():
+                filename = episode.local_filename(create=False, check_only=True)
+                if filename is not None:
+                    gpodder.user_hooks.on_episode_delete(episode, filename)
+
         shutil.rmtree(self.save_dir, True)
 
     @property