Extract exercise settings to own object for json output. Consider also change for db schema.

Start with the course exercise JSON endpoint in the issue and compare its current response with the proposed settings object. Then trace where exercise settings and the database schema are defined. Done means the API shape is agreed and implemented, with any required schema change covered.

The Exercise-objects embedded in the Courses-objects provided by http://tmc.mooc.fi/hy/courses/37.json?api_version=7 are getting pretty large. Would it be possible to embed a further object of some kind in them to hold all these settings? I'm thinking something like this to provide more structure:

{
    "id": 2968,
    "name": "WK1-W1E00.Hiekkalaatikko",
    "locked": false,
    "deadline_description": "2014-09-14 18:00:00 +0300",
    "deadline": "2014-09-14T18:00:00+03:00",
    "checksum": "cd5e2e409e605b535d7eea2bd72231b8",
    "return_url": "http://tmc.mooc.fi/hy/exercises/2968/submissions.json",
    "zip_url": "http://tmc.mooc.fi/hy/exercises/2968.zip",
    "returnable": true,
    "requires_review": false,
    "attempted": false,
    "completed": false,
    "reviewed": false,
    "all_review_points_given": true,
    "settings": {
        "allow_code_reviews": true,
        "allow_feedback": true,
        "allow_return_expired": false,
        "memory_limit": null,
        "runtime_params": [],
        "valgrind_strategy": "fail"
    },
    "solution_zip_url": "http://tmc.mooc.fi/hy/exercises/2968/solution.zip",
    "exercise_submissions_url": "http://tmc.mooc.fi/hy/exercises/2968.json?api_version=7"
}

Thanks to @ljleppan for the idea!