Add Menu+Shift+I shortcut to the Library Manager

Please note that this commit actually adds the shortcut to its menu
entry under the "Tools" menu.

As a side effect, the shortcut tip is only shown in this entry and not
on the another one.

Menu usually means the Ctrl key on most modern systems.

app/src/processing/app/Editor.java

@@ -731,7 +731,7 @@ public class Editor extends JFrame implements RunnerListener {
 
     addInternalTools(toolsMenu);
 
-    JMenuItem item = new JMenuItem(tr("Manage Libraries..."));
+    JMenuItem item = newJMenuItemShift(tr("Manage Libraries..."), 'I');
     item.addActionListener(e -> base.openLibraryManager("", ""));
     toolsMenu.add(item);