v2 -> v3 data migration test scripts

## extract.js
// NUSMods v2 timetable data extractor

var loaderTemplate = data => `
var s = document.createElement('script');
s.src = 'https://cdnjs.cloudflare.com/ajax/libs/localforage/1.5.5/localforage.min.js';

s.onload = function() {
  const data = ${data};
  let count = 0;

  data.forEach(([key, queryString]) => {
    localforage
      .setItem(key, queryString)
      .then(() => {
        count++;

        if (count === data.length) {
          localStorage.clear();
          window.location.reload();
        }
      });
  });
};

document.body.append(s);`;

var s = document.createElement('script');
s.src = 'https://cdnjs.cloudflare.com/ajax/libs/localforage/1.5.5/localforage.min.js';
s.onload = function() {
    const keys = [
        'timetable/2017-2018/sem1:queryString',
        'timetable/2017-2018/sem2:queryString',
        'timetable/2017-2018/sem3:queryString',
        'timetable/2017-2018/sem4:queryString',
    ];
    const data = [];

    keys.forEach(key => localforage.getItem(key)
        .then(queryString => {
            data.push([key, queryString]);

            if (data.length === keys.length) {
                const stringified = JSON.stringify(data, null, 2);
                console.log('Data extracted! Go to https://deploy-preview-518--nusmods.netlify.com/ and paste the code below into the console');
                console.log(loaderTemplate(stringified));
            }
        }))
};

document.body.append(s);