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/singletons/Settings.hpp

@@ -360,6 +360,8 @@ public:
     BoolSetting attachExtensionToAnyProcess = {
         "/misc/attachExtensionToAnyProcess", false};
     BoolSetting askOnImageUpload = {"/misc/askOnImageUpload", true};
+    BoolSetting informOnTabVisibilityToggle = {"/misc/askOnTabVisibilityToggle",
+                                               true};
 
     /// Debug
     BoolSetting showUnhandledIrcMessages = {"/debug/showUnhandledIrcMessages",