Support extensible answer format in config model

[ogallagher]

The wordsearch config file defines each word[-clue] answer as a colon-separated string, but if it's optionally represented with a JSON object {}, then it is more extensible. Some ideas for answer options:

• word: string The answer word/phrase.
• clue: string The shown clue.
• is_template: bool Whether the answer is a template string with {arg1}, {arg2} placeholders.
• template_values: object Values to insert into the template string.

Example:

{
    "word": "I am {number} years old",
    "clue": "I am ___ years old",
    "is_template": true,
    "template_values": {
        "number": ["one","two","three","four","five","six","seven","eight","nine","ten"]
    }
}