Added ability to toggle visibility of tabs (#2600)

This can be done by right-clicking the tab area or pressing the keyboard shortcut (default: Ctrl+U).

Co-authored-by: Leon Richardt <leon.richardt@gmail.com>
Co-authored-by: Rasmus Karlsson <rasmus.karlsson@pajlada.com>

src/widgets/settingspages/KeyboardSettingsPage.cpp

@@ -57,6 +57,7 @@ KeyboardSettingsPage::KeyboardSettingsPage()
 
     form->addRow(new QLabel("Alt + ←/↑/→/↓"),
                  new QLabel("Select left/upper/right/bottom split"));
+    form->addRow(new QLabel("Ctrl+U"), new QLabel("Toggle visibility of tabs"));
 
     form->addItem(new QSpacerItem(16, 16));
     form->addRow(new QLabel("Ctrl + R"), new QLabel("Change channel"));