feat+refactor: trash instance icons

also refactor IconList::deleteIcon

Signed-off-by: leo78913 <leo3758@riseup.net>

launcher/icons/IconList.h

@@ -52,6 +52,7 @@ public:
     bool addIcon(const QString &key, const QString &name, const QString &path, const IconType type);
     void saveIcon(const QString &key, const QString &path, const char * format) const;
     bool deleteIcon(const QString &key);
+    bool trashIcon(const QString &key);
     bool iconFileExists(const QString &key) const;
 
     void installIcons(const QStringList &iconFiles);