Option change previews

[awake]

One of my friends who I asked to install nullpomino suggested to have
a field preview in the general config screen or wherever those options
may be. The field preview will change to give the user feedback on the
options chosen.

The following options should have a field preview:
- show background
- use background fade
- show line effect
- line effect speed
- show meter
- dark next area
- show next above shadow
- next display type
- outline ghost piece
- field bg bright
- block skin (in game tuning)

The sound effects and background music should also have a preview
after the volume is changed, like phones when changing ringtone or
alarm volume.

There are a ton of options in nullpomino and users will feel more
comfortable if they have an instant preview for the options.