StringViewize a bunch of things -- mostly LibGUI

Author: https://github.com/rburchell
Commit: 1024dfa81a
Pull-request: https://github.com/SerenityOS/serenity/pull/170
Reviewed-by: https://github.com/awesomekling

Applications/Terminal/main.cpp

@@ -184,7 +184,7 @@ int main(int argc, char** argv)
     menubar->add_menu(move(app_menu));
 
     auto font_menu = make<GMenu>("Font");
-    GFontDatabase::the().for_each_fixed_width_font([&] (const String& font_name) {
+    GFontDatabase::the().for_each_fixed_width_font([&] (const StringView& font_name) {
                                                        font_menu->add_action(GAction::create(font_name, [&terminal, &config] (const GAction& action) {
             terminal.set_font(GFontDatabase::the().get_by_name(action.text()));
             auto metadata = GFontDatabase::the().get_metadata_by_name(action.text());