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/wizard.py

@@ -272,6 +272,8 @@ class NewWalletWizard(AbstractWizard):
         }
         self._daemon = daemon
         self.plugins = plugins
+        # todo: load only if needed, like hw plugins
+        self.plugins.load_plugin_by_name('trustedcoin')
 
     def start(self, initial_data: dict = None) -> WizardViewState:
         if initial_data is None: