Added ComponentListComponent for laying out elements in a grid and
navigating through them.
Added SliderComponent for selecting from a range of values.
Added SwitchComponent for selecting an "ON" or "OFF" value.
Hooked up GuiSettingsMenu.
Settings now save/load from ~/.emulationstation/es_settings.cfg.
Removed volume from GuiInputConfig since it's in GuiSettingsMenu now.