Move course validation to back-end for efficiency

[canstudios-nicolaw]

Fixes #2487

[tomgreenfield]

Validation is functioning for me – I've been testing by creating a new course and then deleting the page, is this sufficient?

[tomgreenfield]

When attempting to preview a course with no components:

application.js:630 TypeError: Cannot read property '0' of undefined
    at D:\adapt_authoring\plugins\output\adapt\outputHelpers.js:311:17
    at Array.forEach (<anonymous>)
    at iterateThroughChildren (D:\adapt_authoring\plugins\output\adapt\outputHelpers.js:308:11)
    at Object.validateCourse (D:\adapt_authoring\plugins\output\adapt\outputHelpers.js:299:13)
    at D:\adapt_authoring\plugins\output\adapt\publish.js:64:21
    at nextTask (D:\adapt_authoring\node_modules\async\dist\async.js:4578:27)
    at next (D:\adapt_authoring\node_modules\async\dist\async.js:4586:13)
    at D:\adapt_authoring\node_modules\async\dist\async.js:325:20
    at D:\adapt_authoring\plugins\output\adapt\publish.js:59:9
    at wrapper (D:\adapt_authoring\node_modules\async\dist\async.js:272:20)
    at D:\adapt_authoring\node_modules\async\dist\async.js:1639:19
    at wrapper (D:\adapt_authoring\node_modules\async\dist\async.js:272:20)
    at replenish (D:\adapt_authoring\node_modules\async\dist\async.js:439:29)
    at iterateeCallback (D:\adapt_authoring\node_modules\async\dist\async.js:428:21)
    at D:\adapt_authoring\node_modules\async\dist\async.js:325:20
    at D:\adapt_authoring\node_modules\async\dist\async.js:1637:17
    at storeOutput (D:\adapt_authoring\lib\outputmanager.js:132:3)
    at D:\adapt_authoring\node_modules\async\dist\async.js:53:47
    at D:\adapt_authoring\lib\outputmanager.js:188:14
    at D:\adapt_authoring\node_modules\mongoose\lib\model.js:4590:16
    at D:\adapt_authoring\node_modules\mongoose\lib\utils.js:264:16
    at D:\adapt_authoring\node_modules\mongoose\lib\query.js:4326:11
    at D:\adapt_authoring\node_modules\kareem\index.js:135:16
    at processTicksAndRejections (internal/process/task_queues.js:75:11)

[tomgreenfield]

Since the new code is identical to lines 327–331, suggest storing in a variable that can be called:

const appendError = () => {
  errors += app.polyglot.t('app.doesnotcontain', {
    type: parentType[0].toUpperCase() + parentType.slice(1),
    title: parent.title,
    childType: childType
  }) + '\n';
};

[taylortom]

Works for me 👍

Only suggestion I'd make is moving the error info out of 'debug info', as it feels like it's something you'd want to know by default (rather than hiding it).

[canstudios-nicolaw]

I'm not going to get a chance to work on this for a little while. I think it's a good suggestion but it would be worth releasing this as-is for now.