general: Make most settings a BasicSetting

Creates a new BasicSettings class in common/settings, and forces setting
a default and label for each setting that uses it in common/settings.
Moves defaults and labels from both frontends into common settings.
Creates a helper function in each frontend to facillitate reading the
settings now with the new default and label properties.

Settings::Setting is also now a subclass of Settings::BasicSetting. Also
adds documentation for both Setting and BasicSetting.

src/core/hle/service/am/am.cpp

@@ -1443,7 +1443,7 @@ void IApplicationFunctions::PopLaunchParameter(Kernel::HLERequestContext& ctx) {
         params.is_account_selected = 1;
 
         Account::ProfileManager profile_manager{};
-        const auto uuid = profile_manager.GetUser(Settings::values.current_user);
+        const auto uuid = profile_manager.GetUser(static_cast<s32>(Settings::values.current_user));
         ASSERT(uuid);
         params.current_user = uuid->uuid;