Fix 500-link limit for loading training slides from wiki

[ragesoss]

There might be more than 500 training slides linked from https://meta.wikimedia.org/wiki/Training_modules/dashboard/slides

When trying to load training content from the wiki, WikiTrainingLoader does a page link query that does not implement 'continue', so only 500 links are loaded. I think this means that the oldest of the links on the page are the ones that get left out, so the oldest training modules cannot be updated. We discovered that this module errors when you attempt to reload it: https://outreachdashboard.wmflabs.org/training/learning-and-evaluation/using-the-dashboard

If the 500-link limit is the cause as I expect, implementing 'continue' should let us load that module. (Search the codebase for examples of other queries that handle 'continue'.)

[fillingtothemomo]

@ragesoss I have implemented the continue , however I am not sure how to test it locally as I can not navigate to the learning and navigation module on my localhost.

[ragesoss]

@fillingtothemomo to test it locally, you need to first configure your dev environment to use the wiki as the source of training content... I think maybe just setting wiki_education: false in application.yml will do that, as the three config entries for which pages to look for content should already be present.

Then you can attempt to load a single module using the same relative URL as on the production site: /reload_trainings?module=using-the-dashboard. I would expect that to fail in the current version, and work when the continue is implemented.