Define a new Diesel Model for PodcastCover querries.

Define new Diesel Model and impl From<Podcast> trait,
Change the signature of downloader::cache_image function,
Change and merge hammond-gtk::utils::get_pixbuf_from_path functions.

hammond-gtk/src/widgets/show.rs

@@ -10,7 +10,7 @@ use hammond_data::utils::replace_extra_spaces;
 use hammond_downloader::downloader;
 
 use widgets::episode::episodes_listbox;
-use utils::get_pixbuf_from_path_128;
+use utils::get_pixbuf_from_path;
 use content::ShowStack;
 use headerbar::Header;
 
@@ -77,7 +77,7 @@ impl ShowWidget {
         let desc = dissolve::strip_html_tags(pd.description()).join(" ");
         self.description.set_text(&replace_extra_spaces(&desc));
 
-        let img = get_pixbuf_from_path_128(pd);
+        let img = get_pixbuf_from_path(&pd.clone().into(), 128);
         if let Some(i) = img {
             self.cover.set_from_pixbuf(&i);
         }