Everywhere: It's now "Foobar", not "FooBar", and not "foo bar"

I hereby declare these to be full nouns that we don't split,
neither by space, nor by underscore:

- Breadcrumbbar
- Coolbar
- Menubar
- Progressbar
- Scrollbar
- Statusbar
- Taskbar
- Toolbar

This patch makes everything consistent by replacing every other variant
of these with the proper one. :^)

Userland/Applications/Piano/main.cpp

@@ -36,7 +36,7 @@
 #include <LibGUI/Application.h>
 #include <LibGUI/FilePicker.h>
 #include <LibGUI/Menu.h>
-#include <LibGUI/MenuBar.h>
+#include <LibGUI/Menubar.h>
 #include <LibGUI/MessageBox.h>
 #include <LibGUI/Window.h>
 #include <LibGfx/Bitmap.h>
@@ -104,7 +104,7 @@ int main(int argc, char** argv)
     });
     audio_thread->start();
 
-    auto menubar = GUI::MenuBar::construct();
+    auto menubar = GUI::Menubar::construct();
 
     auto& app_menu = menubar->add_menu("File");
     app_menu.add_action(GUI::Action::create("Export", { Mod_Ctrl, Key_E }, [&](const GUI::Action&) {