Parse the theme file.

def parse(theme_file):
    """Parse the theme file."""
    data = util.read_file_json(theme_file)

    if "wallpaper" not in data:
        data["wallpaper"] = "None"

    if "alpha" not in data:
        data["alpha"] = util.Color.alpha_num

    # Terminal.sexy format.
    if "color" in data:
        data = terminal_sexy_to_wal(data)

    return data