Add/remove plugins from GUI

- both internal and external plugins require GUI install
   (except internal HW plugins, which are 'auto-loaded' and hidden)
 - remove init_qt hook
 - in Qt, reload wallet windows if plugin enabled/disabled
 - add 'uninstall' button to PluginDialog
 - add 'add plugins' button to wizard hw screen
 - add icons to the plugin list

electrum/simple_config.py

@@ -346,6 +346,15 @@ class SimpleConfig(Logger):
         assert isinstance(key, str), key
         return self.get(key, default=...) is not ...
 
+    def is_plugin_enabled(self, name: str) -> bool:
+        return bool(self.get(f'plugins.{name}.enabled'))
+
+    def enable_plugin(self, name: str):
+        self.set_key(f'plugins.{name}.enabled', True, save=True)
+
+    def disable_plugin(self, name: str):
+        self.set_key(f'plugins.{name}.enabled', False, save=True)
+
     def _check_dependent_keys(self) -> None:
         if self.NETWORK_SERVERFINGERPRINT:
             if not self.NETWORK_SERVER: